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Late Paleozoic Pelecypods: Pectinacea

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Systematic Paleontology, continued

Family Aviculopectinidae Etheridge, Jr., emend. Newell

Aviculopectenidae, MILLER, 1889, North American Geology and Paleontology, p. 45, (not defined).
Aviculopectinidae, ETHERIDGE, JR., 1906, Mon. Carbo and Permo-Carbo Invertebrata of New South Wales, vol. 2, Pelecypoda, p. 7.

Diagnosis—Pectiniform smooth or ornamented shells, having the two valves more or less dissimilar in ornamentation and convexity; the right valve is the less convex of the two and invariably shows a byssal notch at some growth stage. There is a well defined, flat, smooth, external ligament area on each valve as in Lima or Pinctada, with an oblique subcentral resilifer beneath each beak; with or without additional resilia on either side of the central one. Musculature similar to that in Pectinidae, but lacking the large differentiated dorsal insertions of the circular pallial muscle; in addition, having supplementary pedal muscles in the umbonal cavity, and probably having a small right pedal retractor as well as a larger left one. In some, possibly all, of the genera the inner layer of ostracum is aragonite; ostracum composed of two layers, an outer and inner one neither of which has the foliaceous structure of modern Pectinidae.

Phylogeny of the Aviculopeotinidae

The early history of the Aviculopectinidae is shrouded in mystery, and any statement made at the present time is partly speculative and subject to revision. Too little is known about the hinge characters and ontogeny of early Mississippian forms, and almost nothing is known about the Devonian progenitors of this race.

Most of the genera are well represented in Mississippian rocks. Pernopecten, Annuliconcha, Acanthopecten, Aviculopecten, Limipecten, Streblopteria, Streblochondria, and Obliquipecten are represented among the species described in the great monograph by Hind on the British Carboniferous pelecypods. It is true that almost nothing is generally known regarding the exact stratigraphic distribution of these genera in the Mississippian rocks, but at least it is certain that many of them originated in the Devonian period.

Notwithstanding the fact that. Devonian pelecypod faunas in various parts of the world have been monographed, so little is known about the hinge characters of these pectinoids that I cannot recognize Devonian Aviculopectinidae in the literature.

Ontogeny of Pennsylvanian species furnishes a somewhat tenuous basis for the hypothetical family tree of figure 17.

Figure 17—Hypothetical phylogeny of the Aviculopectinidae, Amussiidae, and Euchondriidae. For Streblopteria, in this diagram, read Clavicosta, and for Clavicosta read Streblopteria.

Hypothetical phylogeny of the Aviculopectinidae, Amussiidae, and Euchondriidae.

Smooth shells, having poorly developed auricles, like Streblopteria s. s., are undoubtedly primitive forms, because they resemble the juvenile parts of so many Aviculopectinidae.

Limipecten and Aviculopecten probably evolved from a form in which at least the right valve was smooth, because the right valves in these two genera are smooth up to a slightly later growth stage than the left valves. It is improbable that either genus gave rise to the other, because the ornamentation of the right valves is different, even at a very early stage. Pseudomonotis, in view of the similar ornamentation on the two valves, was probably derived from a primitive Limipecten lacking well-developed auricles, as suggested by the similarity of juvenile Limipecten to mature Pseudomonotis. The ancestry of Clavicosta is in doubt, owing to the unique ornamentation. In the genus, new costae are added on both valves, during growth, by being inserted or intercalated in pairs. In Limipecten new costae are intercalated singly between preexisting costae. Theoretically the ornamentation of Clavicosta could be developed from Limipecten. by the fission of costae that had been intercalated between older costae.

Acanthopecten had a long history despite my conviction that it is a highly specialized genus. It is well represented in the Mississippian rocks and possibly had ancestors in simplicicostate forms, like the Upper Devonian Aviculopecten ellipticus Hall. The simplicicostate ornamentation, so extraordinary in Paleozoic faunas, points to Acanthopecten as a probable ancestor to the Permian Deltopecten s. s. Likewise, but with less reason, Girtypecten may be a descendant of Acanthopecten.

Subfamily Aviculopectininae Meek and Hayden, emend. Newell

Aviculopectininae MEEK and HAYDEN, 1864, Paleontology, upper Missouri, Smithsonian Contr. Knowledge, vol. 14, No. 172, p. 49.

Acline or prosocline ornamented Aviculopectinidae with a single oblique resilifer located between and mainly behind each beak; in the characteristic genera the outer ostracum in the right valve is prismatic, in the left homogeneous; the inner ostracum is aragonite, either nacreous or crossed-lamellar; prisms of the outer ostracum in the right valve irregular in size and distribution, although there is a gradual increase in size during shell growth; posterior auricle longer than the anterior.

Genus AVICULOPECTEN McCoy, emend. Newell

Aviculopecten, McCoy, 1851, Annals and Mag. Nat. History, 2d ser., vol. 7, p. 171.
Deltopecten, part, of authors.

Acline or only slightly oblique Aviculopectinidae in which the costae on the shell body increase in number on the left valve by implantation, and on the right valve by bifurcation; auricular costae increase only by implantation; new costae appear nearly simultaneously in more or less regular ranks or orders, being introduced at successive stages; costae on auricles and left valve variable in form and spacing, but those of the shell body of the right valve invariably obscure, flat, broad, and closely spaced; number of costae in the two valves about the same; cardinal costae present in both valves of all species, but somewhat variable in prominence; costae when present on the left anterior fold are weaker, irregular and crowded, forming a transitional zone between the ornamentation of the auricle and shell body; ornamentation of left posterior auricle generally set off abruptly by a somewhat coarser posterior costa. of the shell body.

The left valve is generally ornamented in unworn specimens with fine, more or less regularly spaced fila which swing slightly hingewards between costae, or else extend directly across costae and interspaces; acute ventral projections between costae are never present but vaulted spinelike processes arising from imbricating lamellae may occur on the costae, never between them; spines, or concentric ornamentation, save for fila on the auricles, lacking on the right valve. The right valve is nearly flat, rarely concave, left valve markedly convex; posterior auricles generally slightly longer than anterior ones; umbonal folds are more or less distinct, subequal, broadly rounded, the anterior ones being slightly more prominent than the posterior ones and curved forward; posterior umbonal fold of both valves generally nearly straight. Anterior and posterior auricular sulci subequal, those of the right valve being shallower than those of the left.

A comparatively narrow, flat, smooth cardinal area with a sub central shallow, triangular resilifer occurs on both valves, the two resilifers joining at the hinge axis at an angle of 45 degrees, more or less; front and rear margins of resilifers nearly straight and the latter margin is much longer than the former, so that most, but not all of the resilifers lie behind the beaks.

Musculature consists of (1) a relatively large adductor impression with a posterodorsal lobe probably corresponding to a pedal retractor in both valves; (2) a narrow crescentic impression of the gill suspensories below each adductor impression; (3) pallial line unbroken except near its anterior extremity, where it is broken into a series of small pits; (4) two levator pits lying in the umbones; and (5) a very small pit above the adductor impression of the right valve, probably representing a point of attachment of the gills.

Apparently the right valve fits slightly inside the left one because right valves are in many instances smaller than left ones of equal hinge length; furthermore the pallial line and adductor of right valves are closer to the ventral margin than in left ones.

There are two kinds of ostracum in both valves, a thin outer ostracum of calcite, and a thicker, inner ostracum, probably aragonite; outer ostracum apparently homogeneous in left valves, prismatic in right ones; prisms irregularly arranged and somewhat irregular in size, although there is an increase in size from very small ones in juveniles to a diameter of about 30 microns or more in adults; the inner ostracum exhibits two kinds of crossed lamellar structure in exceptionally well-preserved Pennsy lvanian specimens; (1) a concentric crossed lamellar layer which extends to the shell border, externally visible only near the margin of the inner surface of the shell, and (2) an irregular radial crossed lamellar layer covering all the inner surface within the pallial line except the muscle areas; hypostracum part of the shell exceedingly thin. In one species (A. mazonensis Worthen) there is evidence of a periostracum. This species is extraordinary in having a prismatic outer ostracum in the left valve as well as the right one.

The genolectotype is Aviculopecten planoradiatus McCoy, from the Carboniferous limestone of Derbyshire, England.

Range—So far as I can learn, undoubted aviculopectens are not yet known in the Devonian rocks. The demonstrated range of Aviculopecten is early Lower Carboniferous (Mississippian) to Late Permian, inclusive. The so-called aviculopectens that I have seen from the Triassic rocks of the western United States do not show a byssal notch at any stage, and, therefore, belong to some very different group from the Aviculopectinidae.

Discussion—There has been some confusion regarding the identity of the genotype species of Aviculopecten. McCoy clearly intended Aviculopecten docens McCoy to be the type species as pointed out by Girty (1904, pp. 291-296), and practically stated that it was upon this species that the genus was founded (see McCoy 1855, p. 392). However, McCoy's intentions can have no legal bearing in establishing the type of Aviculopecten because he made no mention of the name docens in the original diagnosis of his genus. According to Article 30, Case IIa, paragraph a of the International Rules of Zoological Nomenclature, those species which were not included under the generic name in the original publication are excluded from consideration in determining the types of genera. Anonymous species and species inquirendae are also ineligible for genotype species. McCoy included with the original diagnosis the names of the two species, Aviculopecten planoradiatus and A. ruthveni. The latter has never been designated as the type species so it need not be further considered here. Included in the first diagnosis of the genus was a line drawing of an internal mold labeled Aviculopecten. In a subsequent publication, McCoy (1855, p. 392) explained that this line drawing was made from the type specimen of Aviculopecten docens McCoy, and that it was A. docens that taught him the characters of the genus. In 1889, S. A. Miller (1889, p. 465) made the first unequivocal designation of a type for Aviculopecten, naming A. docens. It appears, however, that A. docens has never been available as the type of the genus, inasmuch as it was not mentioned by name in the first diagnosis of the genus. Zoological nomenclature is not concerned with the biological concept of species, but with the names of species. In 1903, Hind (1903, p. 66) designated A. planoradiatus as the type of Aviculopecten, and this designation appears to be the first legal selection of an available species for the type of the genus.

Chart for Comparison of American Species of Aviculopecten
Aviculopecten s. s. Maximum
H/L HL/L C/H U Body
Special features Age
exemplarius 24 1.14 0.91 0.21 75 43 7 5 Ratio breadth to length ligament area, 0.12 Missouri
arctisulcatus 26 1.08 0.87 0.21 83 38 9 3 Subhemispherical, axis of left rear sulcus near shell body Virgil
occidentalis 29 1.07 0.88 0.17 82 46 9 10 Ratio breadth to length ligament area, 0.07 Missouri
moorei 35 1.07 0.95 0.14 86 46 10 9 Spines numerous Virgil
basilicus 43 1.03 0.79 0.18 85 54 11 7 Costae generally broad, flattened Virgil
sumnerensis 47 1.02 0.73 0.20 93 54 9 12 Umbonal angle Big Blue
mazonensis 34.5 1.01 0.73   90 58 15 20 Ill-defined umbonal folds Des Moines
nodocosta 29 1.15 0.88 0.19 86 52 10 6 Three to five coarse, nodose costae Big Blue
mccoyi 22 1.15 0.73 0.22 85 42 9   Eight or nine coarse, scaly costae Big Blue
vanvleeti 28 1.31 0.80 0.14 71 46 8 6 Small rear auricle, three to five coarse, nodose costae Whitehorse
gryphus 43 1.19 1.03 0.26 80 63 6 6 Acute beak, posterior lobation Word
gradicosta 22 0.98 0.91 0.23 81 64 13 9 Gradation of fine rounded costae in three or four orders Missouri
bellatulus 25 1.08 0.95 0.20 80 93 11 9 Gradation of fine rounded costae in three ranks Kaibab
girtyi 35 1.00 0.77 0.20 87 65 9 8 Five coarse costae, separated by fine ones Word
kaibabensis 60 1.00   0.21 91 85   13 Subhemispherical, posterior fold absent Kaibab
coxanus 14 1.07 0.92   80 46 8 6 Rather shallow marginal sinuses under auricles Des Moines
flabellum 15.5 0.93 0.71   111 38 5 3 Shallow marginal sinuses under auricles Des Moines
germanus 12 1.05 0.81   81 26 6   Shallow marginal sinuses under auricles Des Moines
halensis 7.5 1.05 0.90 0.28 89 24 5 5 Flaring umbonal angle at small size Morrow
phosphaticus 6.2+ 0.84 1.00   90 21 8 6 Large auricles, distinctive shape Phosphoria
peculiaris 40         42     Globular left valve, concave right valve Big Blue
Mean values for mature left valves: H, height; L, length; HL, hinge length; C, convexity;
U, umbonal angle in degrees; A, anterior; P, posterior.
Aviculopecten? ballingeranda (Beede), Aviculopecten coreyanus (White), and Aviculopecten eaglensis (Price) are omitted.

Through the courtesy of the curators of Sedgwick Museum, at Cambridge, England, I have been given an opportunity of examining paratypes of A. docens McCoy and the primary types of A. planoradiatus McCoy. A. docens appears to be a Limipecten, as nearly as I can judge in the absence of any right valves (see pl. 11, figs. 6a-8b).

McCoy's diagnosis of Aviculopecten, based upon this species, is incorrect. It was his belief that a resilifer is absent in Aviculopecten, and subsequent students have accepted McCoy's statement. There is no well authenticated case in the literature of any Paleozoic pectinoid having a smooth ligament area devoid of a resilifer; consequently there is no good reason to suppose that such a hinge structure exists.

The material of A. planoradiatus before me (see pl. 5, figs. 12-15) is too poorly preserved to develop any characters of shell structure, hinge, or musculature, and to that extent the genus Aviculopecten is not well established. The characters of form and ornamentation that can be determined from this type collection correspond so well, however, to the Pennsylvanian group of A. occidentalis Shumard, that I feel justified in drawing a generic diagnosis of the genus based on Pennsylvanian forms as well as the Lower Carboniferous type species. Besides a greater size of its individuals there are two particulars in which A. planoradiatus differs from the Pennsylvanian forms. Introduction of new costae in the British form ceases at a very early ontogenetic stage, whereas, new costae are introduced throughout life in most of the Pennsylvanian species. In A. planoradiatus, the anterior umbonal fold (left valve) overhangs the anterior auricle slightly as in some species of Acanthopecten. It seems hardly likely that these differences alone warrant separating the Pennsylvanian forms from Aviculopecten as a distinct subgenus. I have not been able to see authentic right valves of A. planoradiatus from Derbyshire, England. Hind (1903, p. 68) believed that A. planoradiatus, known only from left valves, is a synonym of A. tabulatus McCoy, described from a right valve. It does not appear that the similarity of ornamentation alone on the type specimens of the two species indicated by Hind is sufficient to class them together, because generally the ornamentation of right and left valves in Aviculopectinidae is conspicuously different. A. tabulatus, however, is clearly congeneric with the American group of A. occidentalis. The only way to show that A. planoradiatus is a synonym of A. tabulatus is to find them associated together in the same beds of Derbyshire, or Parkhill, England.

The characters of hinge, musculature and shell structure given in the preceding diagnosis were taken largely from Aviculopecten exeniplarius, n. sp., but were observed also in some other species.

Of recent years, the term Deltopecten, originally applied to Australian Permian pectiniform shells, has been used for characteristic species of Aviculopecten. This erroneous usage has arisen from the prevailing belief that resilifers are lacking in typical Aviculopecten, whereas they were clearly demonstrated in Deltopecten. Paleontologists have thought to classify most of the Carboniferous pectinoids as Deltopecten. or Aviculopecten, depending upon whether or not resilifers could be demonstrated in them. Consequently, a large number of species in which the hinge characters are not known have been classified as Aviculopecten. Since Deltopecten was the only genus of aviculopectinid aspect known to have resilifers, it seemed logical to classify as Deltopecten all Carboniferous and Permian species known to possess resilifers. In the present work it was discovered that almost all of the Carboniferous forms have resilifers which vary only in detail. The genus Deltopecten, still poorly known, is discussed more fully on another page. Unlike any other Paleozoic form excepting Acanthopecten, the two valves in the type species of Deltopecten are simplicicostate, and furthermore are remarkable in having almost identical ornamentation.

Thus far, the attempts to recognize evolutionary trends in Aviculopecten have been somewhat discouraging. However, the chief difficulty appears to lie in the very large number of genetic lines and the difficulty in obtaining fairly complete stratigraphic series of specimens representative of one line of affinity. For example, I have not been able thus far to secure representative collections of the Aviculopecten occidentalis s. s. gens from Des Moines or Morrow rocks, or post-Des Moines representatives of the distinctive Aviculopecten germanus gens. My results are indicative of untold scores of undiscovered species (or mutations) of Aviculopecten that are to be sought in Pennsylvanian and Permian rocks.

Some suggestion of progressive change within a single gens is suggested by the species Aviculopecten occidentalis, A. basilicus, and A. sumnerensis, named in ascending stratigraphic order. This series, whether or not fortuitous I cannot now say, exhibits increasing average size of individuals and increase in the umbonal angle. During ontogenetic development of any Aviculopecten there is a progressive increase in the umbonal angle, due to the outward curvature of the anterior umbonal fold. Theoretically one might expect to discover evidence that this type of ontogenetic change might be reflected, at least in some series, as a phylogenetic modification.

The species Aviculopecten gradicosta and A. bellatulus are exceedingly alike except that the latter and younger one has a larger number of costae than the former. Since increase in number of costae is an ontogenetic character common to all aviculopectens, we might hope to find that this type of change is also a phylogenetic character.

However, for the greater part, species of Aviculopecten seem to be so isolated and disconnected from each other that the construction of convincing evolutionary series is still a goal to be sought in the future.

Measurements of Specimens in Several Species of Aviculopecten
Species Specimen
No. auricular
No. body costae
at given height
Anterior Posterior Costae Height,
exemplarius L1 17 20.5 1.21 15 0.88 4 0.19 74 6 5 36 20.5 2 0.13
L2 19 23 1.21 18± 0.95±     73± 6 5 36 23    
L3 15± 18.5 1.23 14 0.93 4 0.21 78- 6 4 20 11    
L4 23 24 1.04 20 0.87 4.7 0.20 77   6 51 24    
L5 18± 21 1.17 15.5 0.86 4.8 0.23 74+ 6 5 34 21 1.7 0.11
L6 20 22.5 1.13     4.9 0.22 75 7   37 22.5    
L7 20 21.5 1.07 17.5 0.88     75 6 5 47 21.5    
L8       10                 1.2 0.12
R9 12 13 1.08 14.5 1.21 flat   72± 3 5        
R10       14.5   flat     2          
R11 13 13 1.00 13 1.00 flat   90 3 5        
R12 8 10 1.25 10 1.25 flat     3       0.9 0.09
R13 8.5 9.2 1.08 10 1.18 flat   73± 3 8        
R14 7 8.5 1.21 8 1.14 flat     5          
R15 4 5 1.25 4.5 1.13 flat   65 4          
R16 9.5 10.5 1.12 11 1.16 flat     3 5        
R17 13± 17 1.31 14 1.08 flat             1.3 0.11
R18 14 17 1.22 17 1.22 flat     4          
R19 15 16 1.07 15± 1.00 flat     4          
occidentalis L1 23.5 23.5 1.00 18.5 0.79 3.5 0.15 88 10± 10 51 21 1.5 0.08
L2 26.5 27.5 1.03     5 0.18 80.5   8 42 24    
L3 25 26.5 1.06 23 0.92     81.5 10 10 42 26.5    
L4 24 25 1.04 23+ 0.96 4 0.16 81 10+ 10 47 25    
L5 24 27 1.12         75+     36+ 27    
L6 15.5 17.5 1.13 13.5 0.88     73   9 39 18 0.67 0.05
L7 17 19 1.12 16 0.94     75   12 42 19 1.0 0.06
L8 28.5 29 1.02         84            
L9 24.5 25.5 1.04         86.5 9+ 42 26    
L10 25 26 1.04 23.5 0.94     82.5 8+ 41 26 1.7 0.07
R11 15.7 17 1.08 19.5 1.24     82.5 4 7     1.5 0.07
R12 23 23 1.00 24 1.04     94 3+       1.7 0.07
R13 9 11 1.22 13.5 1.50     78 4 5+        
R14 14.5 16.5 1.14 16+ 1.10     64 4 4        
R15 11± 11± 1.00         64   7+        
arctisulcatus L1 23 23 1.00 21 0.91 5.1 0.22 81 8   38 23    
L2 23± 24.5 1.06 17± 0.74 5.4 0.22 81±   38 24.5    
L3 22 25 1.09 19 0.86     81   39± 25    
L4 20 23 1.15 19 0.95 4.6 0.20 80 10±   38 23    
L5 20 22 1.10 20 1.00     80   30 22    
L6 26 26+ 1.00         83   5 44± 26    
L7 23 24 1.04         83± 2 46± 24    
L8 16+ 20± 1.25 16 1.00 4.0 0.20 73 8 3 30± 20    
L9 22.5 23.5 1.04 19 0.85     84 4+ 34 23.5    
L10 19 22 1.16           7   44± 22    
L11       15       72 7 3        
mazonensis L1 36 34.5 0.96 26 0.72     90 several several 55+ 34.5    
L2 29 28.5 0.98 19 0.66     90± several 18-20 61± 28.5    
L3 23 23 1.00 14.7 0.64     85+ 18± 16± 49± 23    
L4 29 31 1.07 20 0.69     89 17 18± 70 31    
L5 24.5 23 0.94 19 0.78     92 13± 13+ 45+ 23    
L6 17+ 18 1.06 12 0.71     84 11+ 11+ 33+ 18    
L7 19.5 20 1.03 14 0.72     88 11+ 8+ 30+ 20    
L8 33± 31 0.94 22 0.67     95 12± 26± 50± 31    
L9 17 18 1.06 14 0.82     90 13 10± 50± 18    
basilicus L1 42 43 1.02 32± 0.76± 7 0.16 80.5 11 8 50 43    
L2 27 27+ 1.00 24 0.89 5 0.19 78 11   40± 27+    
L3 35 35 1.00 28 0.80 7 0.20 90   5 40 35    
L4 37+ 40 1.04 30± 0.81 0.17 90 11 7 68 40    
L5 38.5 40 1.04     6 0.15 81     54 40    
R6 21 21 1.00 24 1.14     88 6 11     1.5 0.06
moorei L1       30       85 11 11 37 25    
L2   30       4 0.13   9          
L3 20 21 1.05 19 0.95 3 0.14 82 8 10± 37 21    
L4   32   24       81 9   45± 32    
L5 32 35 1.09 30 0.94 4.5 0.13 90 8 6+ 55 35    
sumnerensis L1 39 38 0.97 29 0.74 8 0.20 94 8   48 38    
L2 39     32 0.82     96 12±   52      
L3 35 40 1.14         88 9   52 40    
L4 33 36 1.09     7 0.21 89 9   51 36    
L5 42 44 1.04 29 0.69     96 8 50 44    
L6 46 46 1.00 30 0.65     98 9   41 46    
L7   45             8     45    
L8 43 47 1.09 28 0.65 8 0.18 96 8   64 47    
L9 52 47± 0.90               62 47±    
L10 39 36 0.92 26± 0.66 8 0.20 91 8 14 67 36    
nodocosta L1 26.5 27.5 1.04 22± 0.83 5.5 0.20 90 9 1 53 27.5    
L2 23 26 1.13 21± 0.92 5.2 0.20 86   8 64 26    
L3 16 20 1.25 14.5 0.91 3.5 0.17 80 10±   38± 20    
L4 27 29 1.08 23 0.85 6 0.20 91 11   40 29    
L5 26             90± 11 11 49      
halensis L1 1.00 1.00 2 0.28 94 5 7 27 7    
L2                 5          
L3 7.5 7.5 1.00 6+ 0.80+     98±            
L4 5 5.5 1.10 5+ 1.00     80± 5          
L5   6.5               3+        
L6 7                   21+      
vanvleets L1 25 34 1.36 23 0.92 5 0.14 72   6+ 50 34    
L2 28 30 1.07 25± 0.89 4+ 0.13 74± 10+   50+ 30    
L3 16 19 1.09 11 0.68 3 0.15 76 7+ 5+ 46 19    
L4 27 37 1.37 20 0.74 4 0.10 67     42+ 37    
L5 25 30 1.20 17 0.68 4 0.13 66            
L6 20 22 1.10 16± 0.80     77   5+ 46+ 22    
L7 17 24 1.41 14 0.82 4.5 0.18 65 6   42+ 24    
gradicosta L1 14+ 15 1.00± 13 0.93 3.5 0.23 80 13 12 62 15    
L2 21 22 0.96 18.5 0.88     82 13± 5+ 66 22    
gryphus L1 26 33 1.26 27± 1.03 7.5 0.22 80 6+ 6+ 63 33    
L2 33 43 1.30                      
L3 25 27 1.08     8 0.29              
flabellum L1 14 12 0.85 9 0.64     114 4 3 36+ 12    
L2 5 4.9 0.98 4.8 0.96     94 3   23 4.9    
L3 13 13 1.00 10 0.77     112 3   39 13    
L4 17 15.5 0.91 13+ 0.76           36± 15.5    
L5 12 11 0.91         113 6   36 11    
L6 11 10 0.91 8 0.72     107   3 37 10    
germanus L1 11 12 1.09 8 0.72     79± 6 30 12    
L2 10 11 1.10 9 0.90     75-82 7 25 11    
L3 5 5+ 1.00 4.5 0.90     83 5+ 22± 5+    
L4   10   7             10    
L. Left valves. R. Right valves.


Plate 1, figures 12, 17; Plate 3, figures 1-12; Plate 4, figures 10-12

Moderate sized aviculopectens, rarely higher than 25 mm., as a rule less than 20 mm., generally slightly higher than long and moderately incised below the auricles; obliquity, acline or slightly prosocline; axis of left posterior sulcus nearly bisecting auricles; left umbonal angle about 75 degrees; convexity ratio (convexity/height) in mature undistorted left valves, 0.19 to 0.23. There are five to seven, generally six, rounded costae on the left anterior auricle, four or five of which are primary ones and the others secondary, grading into two to four small, irregular, crowded, transitional costae on the outer slope of the umbonal fold. Costae of the shell body rounded, low, generally as broad or broader than the interspaces, 34 to 50 of them, in mature specimens, including transitional costae in left valves, distributed in three or four ranks of intercalaries; four to six fine costae occur on the left posterior auricle, becoming obsolete at an intermediate growth stage, so that, except in rare cases (two out of twenty specimens), the mature part of the auricle is smooth; spines absent, imbrications mayor may not occur on the anterior part of the shell body and on the anterior auricle of the left valve.

Figure 18—Early growth stages of the beaks of Aviculopecten exemplarius Newell, n. sp. Upper, left valve, X 24; the concentric lines represent those growth lines which were sufficiently prominent to be followed; the radial costae do not appear until a shell height of 0.5 mm. is attained. Lower, right valve, X 24; the shell is practically smooth until the broad, flat costae appear at a height of about 1 mm. [Images scaled and magnifications adjusted for web presentation.]

Early growth stages of the beaks of Aviculopecten exemplarius Newell, n. sp.

The fila are fine, about 10 in a space of 1 mm., occurring on the juvenile parts of the shell body in exceptionally well-preserved specimens, but give way to irregular growth lines at a height of 20 mm. or so; ligament area extraordinarily broad, attaining as much as 2 mm. at a shell height of 20 mm. Shell substance of either valve divisible into four layers (1) a thin outer layer, homogeneous in the left valve, prismatic in the right valve; (2) a concentrically crossed lamellar layer which extends to the border of the shell; (3) an irregular radially crossed lamellar layer covering the inner surface within the pallial line except that part occupied by (4) a thin hypostracum layer of the adductor impression. Musculature: large retractor impression with a postero-dorsal lobe corresponding to the pedal retractors, narrow imprint of the gill suspensories below and to the front of either adductor; pallial line unbroken expanding into a relatively broad impression under the adductor; two levator pits in the umbones; a small pit of the superior gill suspensories above either adductor.

Figure 19—Dorsoventral section, X 8, through a mature left valve of A. exemplarius Newell, n. sp. The complete shell thickness is represented. [Images scaled and magnifications adjusted for web presentation.]

Dorsoventral section, X 5, through a mature left valve of A. exemplarius Newell, n. sp.

Figure 20—Anteroposterior sections across the ventral margin in mature Aviculopecten exemplarius Newell, n. sp., X 16. A, Left valve; B, right valve. [Image scaled and magnifications adjusted for web presentation.]

Anteroposterior sections across the ventral margin in mature Aviculopecten exemplarius Newell, n. sp.

Measurements of specimens of Aviculopecten exemplarius are given in the table previous.

Comparison—This species is closely similar to Aviculopecten arctisulcatus, n. sp., found at a higher horizon, but well-preserved specimens of the two species generally can be distinguished. The following differences are the more obvious ones for undistorted specimens:

A. exemplarius, n. sp. A. arctisulcatus, n. sp.
a. Axis of left posterior sulcus bisects auricle. a. Axis of sulcus close to posterior costa of shell body. Left posterior auricle flattened.
b. Beaks and umbonal slopes slightly compressed, convexity decreasing rapidly toward center in left valves. b. Left valves slightly tumid to hemispherical.
c. Spines and imbrications rare. c. Posterior spines common on left valve, imbrications common on left anterior auricle.
d. Posterior auricular costae become obsolete at an intenuediate growth stage. d. Posterior auricular costae either faint, extending to margin, or entirely absent.
e. Umbonal angle commonly about 75 degrees in adults. e. Umbonal angle as a rule about 80 degrees in adults.
f. Filose ornamentation restricted to juvenile parts of shell. f. Filose ornamentation extends into mature stage.

It can be most readily distinguished from A. mazonensis by the ornamentation of the left rear auricle and- the angularity of the posterior umbonal fold on the left valve.

Material—The species A. exemplarius is founded upon several scores of fine specimens of both right and left valves (Kansas Univ. Paleont. Type Coll., No. 233) obtained at a single locality and horizon. The preservation of the shell substance is not excellent, although the various elements characteristic of Aviculopecten can be recognized.

Occurrence—Upper Carboniferous. The type lot was collected from a cross-bedded limestone consisting of brown limestone pebbles, comminuted shells, and oolite grains, a local limestone in the Bonner Springs shale (Missouri subseries) near Bonner Springs, Kansas. There are rare pebbles of a greenish rock resembling glauconite, and grains of sphalerite that appear to be worn. Other specimens were found in oolite, impure limestones, and limy shales. The limestone bed, occurring just below the Platt.sburg formation, is a basal conglomerate and marks an unconformity at the top of the Bonner Springs shale.

Other specimens referred to this species have been found in the oolitic Drum limestone near Independence, Kan.; Vilas shale, Louisville, Neb. (Murphy quarry); Captain Creek limestone, (Kiewitz quarry) Louisville, Neb.; South Bend limestone, 2 miles northwest of Nehawka, Neb.; questionably from the Rock Lake shale, 2 miles east of Louisville, Neb.; Rock Lake shale near Bonner Springs, Kan.; and South Bend limestone near Lansing, Kan.; Graford formation, McKenzie Mt., Palo Pinto county, Texas; and Graford formation near Brownwood cemetery, Brown county, Texas. All of these occurrences are of Kansas City or Lansing age (Missouri subseries, Pennsylvanian).


Plate 4, figures 1- 3

Medium-sized aviculopectens ranging in height up to 26 mm., suborbicular, with moderately deep auricular sinuses; obliquity acline; axis of left posterior sulcus relatively close to the umbonal fold, that is in every case below (ventral to) the bisectrix of the auricle; left umbonal angle generally slightly above eighty degrees; convexity ratio (convexity/height) in well preserved adult specimens 0.20 to 0.22; costae of left anterior auricle rounded and closely spaced, 7 to 10 in number, most commonly 8. In a single right valve in which the anterior auricle could be studied, there were four costae; generally two or t.hree irregular crowded costae on the left anterior umbonal fold that form an illdefined transitional zone between the slightly coarser ornamentation of the shell body and front auricle; 30 to 46 broadly rounded low costae on the shell body, as broad and generally broader than the interspaces, distributed in three or four successive orders; posterior auricles either entirely smooth or there may be two to five faint broad costae that extend completely across the auricle; spines occur in many instances along the distal parts of the posterior costae in the shell body of the left valve, less commonly on other parts of the left valve; roughened imbricated lamellae common on the left anterior auricle and adjoining parts of the left valve; surface of unworn left valves covered with fine fila numbering, in the specimens measured, from about 10 to 15 in the space of 1 mm., those fila near the ventral margin being progressively more widely spaced; ligament area, observed in only one specimen, broad, ratio of breadth to length about 0.10; prisms at ventral margin of outer shell layer in full grown right valve range from 15 to 25 microns in diameter.

Figure 21—Anteroposterior section across ventral margin in left valve of mature Aviculopecten arctisulcatus Newell, n. sp., X 19. Only the outer ostracum is preserved, the inner, aragonitic layer having been dissolved. [Image scaled and magnifications adjusted for web presentation.]

Anteroposterior section across ventral margin in left valve of mature Aviculopecten arctisulcatus Newell, n. sp.

Measurements of specimens of Aviculopecten arctisulcatus are given in the table previous.

Comparisons—From similar species, such as A. exemplarius, the present form is distinguished by the following characters: the posterior sulcus has its axis almost against the posterior costa of the shell body; the form is more tumid in undistorted shells, in some instances nearly hemispherical; posteroventral spines are commonly present; posterior auricular costae are few and faint or entirely absent, in no case becoming obsolete at an intermediate growth stage; the number of costae on the anterior auricle of the left valve is uniformly high; unworn shells exhibit regular filose ornamentation on auricles and shell body of left valve.

Material—The species A. arctisulcatus is based on several scores of specimens, mostly incomplete, from a single locality (Kansas Univ. Paleont. Type Coll., Nos. 234, 235). The preservation of these specimens is such that only the thin outer shell layer remains, all inner structures having been lost by solution of the crossed-lamellar and hypostracum layers of the shell.

Occurrence—Upper Carboniferous. The type collection was found at or near the horizon of the Brownville limestone (upper Wabaunsee), 1 mile north of Reece, Kan., on U. S. highway 54. The rock is a gray to buff, fine-grained, hard, argillaceous limestone in which shells of various kinds are common. Right valves are rare and poorly preserved, but in almost every instance the existing right valves are nearly in apposition with left valves, indicating quiet water conditions. Other specimens referred to the same species were found at Brownville, Neb., exact horizon unknown; Houchen Creek limestone, 1 1/2 miles east of Paxico, Kan.; Aspinwall shale south of Nemaha City, Neb., and 1 1/2 miles north of Brownville, Neb.; a single specimen said to come from the Florena shale at Grand Summit, Kan., is a characteristic representative of the species. Questioned identifications were made of specimens from the Rock Bluff limestone member of the Deer Creek limestone, Big Springs, Kan.; Fort Riley limestone member of the Barneston limestone, Marysville, and Junction City, Kan.; Neva limestone, member of the Grenola limestone, sec. 30, T. 7 N., R. 30 E., Nebraska; Florena shale member of the Beattie limestone, Beaumont, Kan. These horizons are in the Virgil (Shawnee, Wabaunsee) and lower Big Blue beds.


Plate 4, figures 4-9; Plate 5, figure 7

Pecten occidentalis Shumard, 1855, Missouri Geol. Survey, Ann. Rept., p. 207, pl. c, fig. 18.

Shell ranging in height up to 28 mm. in large adults; suborbicular, slightly higher than long, with rather deeply incised sinuses at the margin of each auricle; acline, rarely with distinct prosocline obliquity; axis of posterior sulcus approximately bisecting the rear auricles; umbonal angle in full-sized specimens generally more than 80 and less than 85 degrees; convexity ratio in undistorted left valves (convexity/height) ordinarily between 0.15 and 0.18; from 8 to 10 rounded costae occur on the left anterior auricle, half of which are of the first order, the remainder, second order; there are generally 40 to 50 moderately narrow and elevated costae on the body of the shell, which are crowded and irregular over the anterior umbonal fold forming a transition to the more regular ornamentation of the auricle; 9 or 10 fine costae occur across the posterior auricle; commonly there are small stublike spines on the coarse posterior costae of the shell body in the left valve, and small spines and projecting imbricate lamellae are usually found on the front umbonal fold and anterior auricle of the left valve, less commonly on the posterior auricle; fine regular fila occur on all parts of an un abraded shell, spaced about 15 in 1 mm. over mature areas of the shell body; ligament area narrow, less than 2 mm. in large shells.

Figure 22—Anteroposterior section across the ventral margin of the left valve in mature A. occidentalis (Shumard), X 19. [Image scaled and magnifications adjusted for web presentation.]

Anteroposterior section across the ventral margin of the left valve in mature A. occidentalis (Shumard).

Measurements of specimens of Aviculopecten occidentalis are given in the table previous.

It is with little hesitation that I have employed Shumard's name for this species, even though the original types, formerly located at Washington University, St. Louis, were long since destroyed by fire. Insofar as the species is not based upon existing types, it is poorly founded. On the other hand, Shumard illustrated the original type specimen and stated that it was found "by Mr. Hawn, in the Coal Measures, near Plattsburg, in Clinton County," Mo. The rocks near Plattsburg, Mo., are included in the Kansas City and Lansing groups. In the collections before me there is a well-defined species corresponding fairly well to Shumard's illustration. This form is common in beds of Kansas City age, and in Kansas is replaced above by another form, A. exemplarius, n. sp. There appears to be good basis for the continued recognition of the name occidentaiis, and consequently I do not now feel justified in abandoning it.

Comparison—This species is distinguished by its upright form, acuminate posterior auricles, moderate size, orbicular shape, low convexity, rather large umbonal angle (75 to 88 degrees), large number of costae on the left anterior auricle, by the common occurrence of projecting imbrications over the surface of the anterior part of the left valve, by the narrowness of the ligament area, and by the moderately slender costae. The form most like A. occidentalis is A. moorei. The latter is distinguished by a much greater profusion of spines and by a considerably greater average size.

Material—The above description was drawn up from more than 100 specimens from the Westerville oolite (Kansas City group) at several localities near Kansas City.

Occurrence—Upper Carboniferous. The species is abundant in the oolitic division of the Westerville formation (Kansas City group) near Kansas City, but rare in nonoolitic parts of the division; common in the oolitic Farley limestone (Kansas City group) of the same area; Captain Creek limestone (Lansing group) in the quarries near Louisville, Neb. Right valves are not uncommon in the oolite occurrences, but are not found in apposition to left valves. The separation of the valves, in harmony with the pronounced cross-bedding of the oolite, indicates an environment of marked current action and shifting sediments. It is questionably identified because of insufficient material from the Bethany Falls limestone (Bronson group) at Birmingham, Mo., and Lane shale (Kamas City group), Kansas City, Mo.


Plate 6, figures 4-6

This form is very like A. occulentalis (Shumard), and is to be distinguished from the latter by a considerably larger size and a greater development of spines along the anteroventral part of the left valve. The costae are moderately high and rounded in most specimens, but a few individuals have somewhat depressed and broad costae. During the development of a shell, spines appear first on costae along the anterior and posterior margins of the shell body in the left valve, and on the anterior auricle.

Figure 23—Anteroposterior section across the ventral margin of left valve in mature A. moorei Newell, n. sp., X 19. Only the outer ostracum is preserved. [Image scaled and magnifications adjusted for web presentation.]

Anteroposterior section across the ventral margin of left valve in mature A. moorei Newell, n. sp.

During continued growth more spines are added on these areas and appear on costae progressively farther and farther inward from the front and rear margin. Generally, only the larger and older costae bear spines. Near the ventral margin every third or fifth costa on the front part of the shell has spines. Spines occur in some cases across the middle part of the ventral edge. The average height in a number of the largest specimens is 35 mm., or slightly more. The prisms of the outer ostracum at the ventral border in a right valve 23 mm. high, range from 10 to 25 microns in diameter.

The name of this species is given in honor of Dr. R. C. Moore.

Measurements of specimens of Aviculopecten moorei are given in the table previous.

Comparison—This species is very much like A. occidentalis (Shumard) and actually may be a descendent of it. The characteristic development of spines and large size distinguish A. moorei from A. occidentalis. The spiny ornamentation and usually fewer costae separate A. moorei from A. basilicus. There is some variation in spinosity in both A. occidentalis and A. moorei. Occasional specimens of the former species exhibit a few spines along the front margin of the left valve, but smooth individuals are more common. Entirely smooth specimens of A. moorei are rare.

Material—The new species is based on some 30 specimens from the Oread formation at several localities in Nebraska. The inner ostracum has been dissolved from all of the specimens, leaving only the film of outer ostracum of both valves. (Types, Yale Univ., Peabody Mus., No. 14,452.)

Occurrence—Upper Carboniferous. The type specimens were obtained in gray and buff argillaceous limestone filled with shell fragments of various kind of pelecypods. This limestone occurs as lenses just above the Plattsmouth member of the Oread formation (lower Shawnee group) near Nehawka, Neb., a horizon probably equivalent to the Kereford limestone. Other specimens were found in the Plattsmouth member of the Oread formation at Lecompton, Kan.; Lawrence shale, Lawrence, Kan.; Iatan limestone, and Tecumseh shale, both near Nehawka, Neb.; Kereford limestone, Amazonia, Mo. All of these occurrences are in the Douglas and lower Shawnee groups, Virgil subseries, Pennsylvanian.


Plate 6, figures 13-16b

This robust species is similar to A. moorei and A. occidentalis (Shumard) in general aspect, but is readily distinguished by a greater average size, generally broad, flattened costae, and an almost complete absence of spines or projecting imbrications. I have several specimens having a height of at least 35 mm. The holotype and one paratype, both left valves, show an extraordinary tendency for the broader ribs to split distally into two or three smaller ones. The fission of the costae occurs at a late ontogenetic stage and may be regarded as a gerontic character.

Figure 24—Anteroposterior section across the ventral margin of left valve in mature A. basilicus, n. sp., X 19. [Image scaled and magnifications adjusted for web presentation.]

Anteroposterior section across the ventral margin of left valve in mature A. basilicus, n. sp.

Measurements of specimens of Aviculopecten basilicus are given in the table previous.

Material—The species is based on nine specimens representing two collections from widely separated localities. Holotype and topoparatypes, Kansas Univ. Paleont. Type Coll., No. 369. Paratypes, Yale Univ., Peabody Mus., No. 14,45l.

Occurrence—Upper Carboniferous. The holotype and some paratypes retaining the complete ostracum occur in a gray, fine, sandy oolitic limestone of the Haskell limestone (Douglas group) at a spring on Cameron's Bluff near Lawrence, Kan. Other paratypes, in which only the outer ostracum is preserved, were collected from an argillaceous and ferruginous calcareous rock of the Graham formation (Cisco), 2 1/2 miles west of Lacos, Tex. The Graham shale is probably of Douglas or Shawnee age, Virgil subseries, Pennsylvanian.


Plate 6, figures 7 -10

This form is very like A. arctisulcatus in many particulars. It differs conspicuously in having from three to five of the first order costae much coarser than the others, these costae being provided with one or two coarse spines, the bases of which produce knotty protuberances, broader than the costae on which they occur. The umbonal angle is flared outward and relatively large in mature specimens because of an excessive outcurving of the anterior umbonal fold. The costae are either elevated and narrow, or broad and flattened, and in either case are somewhat more numerous than in similar species.

Measurements of specimens of Aviculopecten nodocosta are given in the table previous.

Comparison—This species is similar to A. arctisulcatus, its differences from that species being indicated in the foregoing description. From A. mccoyi M. and H. it differs in having a large umbonal angle, more costae, and fewer coarse spinose costae.

Material—The new species is based on seven specimens, six from one locality and horizon, and one from another horizon. (Holotype and topoparatypes, Yale Univ., Peabody Mus., No. 14,453. Paratype, Kansas Univ. Paleont. Type Coll., No. 367.)

Occurrence—Lower Permian. The holotype and topotype were found in fine-grained, ferruginous, argillaceous limestone belonging to the Burr member of the Grenola limestone (Council Grove group, Big Blue series), at the southwest edge of Burbank, Okla. A paratype was found in fine, calcareous, gray shale of the Florena member of the Beattie limestone (Council Grove group), at Grand Summit, Kan.


Plate 6, figures 1, 2

Suborbicular, acline, medium sized aviculopectens with a very acute posterior auricle; umbonal angle about 80 degrees, with both umbonal folds of the left valve nearly straight; convexity ratio (convexity/height) 0.23 or slightly less; 13 high and rounded costae, of which 6 are primary ones, occur on the left anterior auricle and about the same number ornament the posterior auricle; left anterior fold well defined, subangular, body of shell smooth or occupied by three or four transitional costae, including transitional ribs with 62 to 66 narrow and high costae of which the posterior one is a coarse one of the first order; introduction of new costae exceedingly regular, each costa increasing rapidly in height so that there is a marked gradation in coarseness from first order costae down to those of the fourth order; costae crossed by fine, regular fila which produce small scalelike projections on the smaller costae and rise into coarser scales over the larger ones.

Figure 25—Anteroposterior profile across the surface of the ventral margin in left valve of A. gradicosta Newell, n. sp. [Image scaled and magnifications adjusted for web presentation.]

Anteroposterior profile across the surface of the ventral margin in left valve of A. gradicosta Newell, n. sp.

Measurements of specimens of A. gradicosta are given in the table previous.

This form belongs to the heterogeneous group generally classified as Aviculopecten mccoyi M. and H., but is readily distinguished from that form by the numerous and high costae.

Material—The species is described from two specimens collected at two different horizons (Kansas Univ. Paleont. Type Coll., holotype, No. 365; paratype, No. 366).

Occurrence—Upper Carboniferous. Paratype in cross-bedded, sandy, oolitic limestone of the South Bend limestone member (Stanton limestone) Lansing group), Fredonia, Kan.; holotype found in cross-bedded, oolitic limestone, Westerville oolite (Kansas City group), Turner, Kan. Missouri subseries, Pennsylvanian.


Plate 4, figures 15, 16

Deltopecten eaglensis Price, 1916, West Virginia Geol. Survey, Rept. on Raleigh, Mercer, and Summers counties, p. 719, pl. 31, figs. 1, 2.

Price's description:

Shell small, suboval, slightly oblique and inequilateral, height equal to or a little more than the greatest length of the shell below, length of hinge line unknown, probably two thirds to three fourths of this dimension, which is measured in a direction such that its prolongation would meet the extension of the hinge line at a point about 30 millimeters in front of the beak; left valve depressed, convexity greatest at the midheight, beak small, pointed, extending slightly beyond the hinge line, separated from the ears by a sinus on each side; the anterior ear wedge-shaped, raised above the narrow, deep sinus, its surface slightly convex, its lateral margin curved. inward from the hinge line at an angle of about 65°; posterior ear depressed, its surface flat, not raised above the bottom of the sinus which separates it from the body of the shell, its lateral margin concave, posteriorly acuminate at the hinge line, larger than the anterior ear, Posterior sinus curving slightly inward. one fifth longer than the anterior sinus, which also curves slightly inward. Ventral margin broadly rounded. very nearly semicircular. Surface of this valve ornamented by sixteen fine, raised, rounded costae, half of which originate within one or two millimeters, and the other half within five millimeters, of the beak; costae separated by broad. flat spaces from two or three times their width, beyond which at the ventral margin they are slightly produced, giving the border a scalloped appearance, but without any evidence of spines at the extremities of the costae; crossing the latter are extremely fine, concentric striae, slightly imbricated, incurved and crescentic on each intercostal space. occasionally more prominent than the average with small protuberances where they cross the costae, in this respect resembling Acanthopecten carboniferus, but with no evidence of spines. Two radiating costae appear upon the anterior ear and the fine concentric striae cross the posterior ear parallel to its outer margin. On this ear the radiating costae are almost obsolete.
This species very nearly resembles in size, configuration, and ornamentation Aviculopecten arkansanus Mather, with the following differences. noted after a comparison with Mather's type specimen, kindly loaned by the Walker Museum of the University of Chicago. Our shell is depressed, its beak not full, its convexity about one half that of atkansanus, no concentric striae appearing on Mather's specimen, which is a cast, in a limestone matrix, of the exterior of a left valve. The absence of these striae may be due merely to their not having been preserved on the exfoliated shell. Our shell is slightly broader, proportionately. at the ventral extremity. but the ventral margin of Mather's specimen is not entire and may not exhibit the true outline. . . .
Dimensions of Two Specimens:
Hinge line,
7 8 1 ..
9 .. 1 5.5

The types of A. eaglensis are lost, at least temporarily. Mr. Dana Wells generously made an extensive search for them at West Virginia University, where they are supposed to be located. Price's comparison of A. eaglensis with A. arkansanus Mather was rather futile because he thought that the type of A. arkansanus is an external mold. It is, however, a complete left valve buried in matrix so that only the inner surface is exposed. This was particularly obvious when the holotype of A. arkansanus was examined under xylol. Naturally, a squeeze of the interior of the type specimen of A. arkansanus does not show the external shell ornamentation. A. eaglensis is like A. halensis Mather, differing principally in having a smaller angle and fewer costae. It may be that the three species A. halensis, A. arkansanus, and particularly A. eaglensis, were based on juvenile specimens. An exact understanding of these forms must await the discovery of further topotypes.

Occurrence—The figured syntypes of Aviculopecten eaglensis (Price) are said to have been found in the Eagle limestone, of Pottsville age, at Eagle, Fayette County, West Virginia.

According to Dr. Harold Wanless (personal communication),

the Eagle limestone is in the upper Pottsville (lower Pennsylvanian) several hundred feet below the horizon of the Seville limestone of Illinois. It is considerably older than the Bevier coal section and may not be represented in the northern Mid-Continent region.


Plate 6, figure 3

Aviculopecten phosphaticus Girty, 1910, U. S. Geol. Survey, Bull. 436, p. 43, pl. 4, fig. 11.

Girty's description:

Shell small, subquadrate, slightly wider than high and somewhat oblique. Hinge line longer than the greatest width.
Left valve rather strongly convex. The ears are triangular, depressed. Anterior ear oblique, more depressed than the posterior, defined in outline by a deep sinus. The posterior ear is defined from the rest of the shell by an angulation and in outline by a moderately strong sinus.
The sculpture consists of rather thin, high, abruptly elevated, subequal costae, separated by relatively very broad, flat striae. On the body of the shell the costae are 21 in number. Toward the anterior side they become more closely arranged or rather, perhaps, one or two alternating ones are introduced. The anterior ear has seven or eight fine, rather closely arranged radiating costae, but there is a space between the ear and the body of the shell which is not thus ornamented. The same is true of the posterior ear, only the space is broader and the ear is sharply defined on the body of the shell by the angulation above mentioned. The posterior ear bears six costae not so closely arranged as those on the anterior. There is also a concentric ornamentation of fine lirae much more crowded than the costae. These are conspicuous on the noncostate strip which defines or forms part of the posterior ear. They are present on the latter as well. and also on the anterior ear, but only traces of them can be seen crossing the body of the shell in the only specimens examined.
Right valve unknown.

After studying a squeeze of the holotype, there is nothing that I can add to Doctor Girty's description. The shape of this species is distinctive. Whether or not the holotype is a normal representative of the species cannot be ascertained until additional topotypes can be obtained and described. (Holotype, U. S. Geol. Survey, No. 1,737.)

Occurrence—Permian. The type specimen came from the phosphate beds of the Phosphoria formation, Thomas Fork, Wyo. U. S. Geol. Survey, sta, 988c.


Deltopecten ballingerana Beede, 1916, Indiana Univ. Studies, vol. 3, p. 10 (not figured).

Beede's description:

The shell is large, nearly as high as long, rather convex, slightly oblique, with the hinge nearly as long as the shell. The ears of the left valve are large, the anterior one being separated from the shell by a rounded. rather indefinite sulcus, with considerable marginal construction below it. The posterior ear is apparently somewhat longer than the anterior one, and terminates with a sharper angle. It is less sharply separated from the shell and has a broader marginal sinus below it. The anterior ear of the right valve is separated from the shell by a deep marginal sinus extending more than half way to the beak.
The body of the right valve is ovate in outline, most convex above 'the middle, with the beak projecting slightly above the hinge. The anterior part of the larger specimens possesses a wide zone of stronger growth marks and fainter radiating sculpturing than is found on the rest of the valve. The surface of the valve is covered with three ranks of radiating costae. The largest, eight to twelve in number, appearing at rather wide intervals, reach the beak. Between the larger costae there are from two to six smaller costae. All these ribs are split, each one being doubly carinated at its crest, or it is formed of two similar ones, giving the shell a unique appearance. These costae extend over the ears, being much stronger on the anterior one, on which seven or eight can be counted while four or five faint ones appear on the posterior ear. Both coarse and fine growth lines ornament the valve. The former are rather conspicuous and are rather widely spaced. The larger costae are very indistinctly developed on the posterior half of the shell and are quite prominent on the anterior half. There seems to be some evidence that the surface was roughened by vaulted lamellae, but not markedly so.
A faint impression of the right valve shows it to be very flat. and to be marked by nearly even radiating costae of moderate size. Other characters are not well shown. Length of shell about 60 mm.; height. 51 mm.; convexity of left valve, 7 mm. Smaller specimen. hinge is 31 mm.; height of same specimen, 40 mm.; length of shell, 39 mm.
This species is similar in outline and superficial appearance to D. texanus, Girty. from the rocks below, but its unique split-rib ornamentation and probably thinner shell separate it at once from that shell.
Quarries in the west part of Ballinger, Texas, on the north side of the Colorado river.

Comparison—There is no described species with which I am acquainted having the above characters of ornamentation. Indeed, lacking authentic specimens and illustrations of the species, it cannot be placed in any of the known generic groups.

Material—The types appear to be lost, at least temporarily, although I have made every effort to locate them. On the other hand, the exact locality from which the types were secured is known and eventually the species may be redescribed and adequately figured on the basis of topotype specimens.

Occurrence—Permian. Arroyo formation, quarries in the west part of Ballinger, Tex., on the north side of the Colorado river.


Plate 4, figures 13 a, b, H

Aviculopecten germamus Miller and Faber, 1892, Cincinnati Soc. Nat. History, Jour., vol. 15, p. 81, pl. 1, fig. 9.

Small subquadrate, acline or slightly prosocline shells with large distant costae of which there are at least two orders, the second order being introduced by intercalation. The most distinguishing feature is the very shallow posterior sinus bounding the rear auricle and the resulting quadrate form of the auricle. An extraordinary fold and faint crest occurs about midway along the posterior margin of the posterior auricle. There is no distinction between the ornamentation of the posterior auricle and the shell body, but there appears to be a transition zone of ornamentation in the well-defined anterior auricular sulcus where the costae become crowded and obsolescent. No well-defined posterior sulcus, the flattening of the auricular area taking place rather gradually. The shell substance shows distinctly a rather coarse concentric crossed-lamellar structure with a poorly defined rhombic pattern.

There are growth lines in the lectotype on the outer surface of the crossed-lamellar layer, suggesting that this was the original surface of the shell and that there was no outer ostracum layer. This would be an anomalous condition in a Paleozoic pectinoid, and since the shells are somewhat worn, their original structure cannot be positively determined. One badly exfoliated specimen appears to show traces of an oblique resilifer, like that in the Aviculopectinidae, and for that reason these shells are classed as Aviculopecten, although their peculiar shape suggests that they might eventually prove to belong to some other group.

The lectotype exhibits a few spines along the ventral margin and particularly along the posterior part of the ventral edge. The spines are short, blunt, and are continuations of the costae. The abrupt appearance of the spines, together with a marginal weakening of the sculpture, suggests that the lectotype is a mature or even gerontic individual. The convexity on the lectotype is 2 mm. Right valve unknown.

Measurements of specimens of Aviculopecten germanus are given in the table previous.

Comparison—There is no described American Pennsylvanian species that is likely to be confused with this one. The curious shape of the rear auricle suggests some of the Pterinopectinidae, and it is possible that better preserved specimens will show that the species belongs to that group.

Material—The specimens before me are four syntypes (Chicago Univ., No. 8,778) generously lent me from Walker Museum by Dr. Carey Croneis. The specimens are badly preserved left valves. The best specimen, plate 4, fig. 13, is here selected as the lectotype.

Occurrence—Upper Carboniferous. The types occur in a matrix of black, pyritiferous, fine-grained, possibly concretionary limestone. According to the labels accompanying the type specimens, they were found by Faber in Pennsylvanian rocks (lower Pennsylvanian) along Elkhorn Greek, Kentucky.

Dr. Harold Wanless writes as follows:

I presume this refers to Elkhorn Creek in the Eastern Kentucky Coal field. This is in Letcher and Pike counties, eastern Kentucky. The marine horizons exposed there are a dark shale of the Amburgy coal, which probably corresponds with our Seville limestone of coal No. 1, Illinois, and one or two lower marine horizons. They are all upper Pottsville.


Plate 4, figure 23

Aviculopecten coxanus Meek and Worthen, 1860, Philadelphia Acad. Nat. Sci., Proc., p. 453; 1866, Illinois Geol. Survey, vol. 2, p. 326, pl. 26, figs. 6a, b.

The holotype is a small, acline left valve especially distinguished by having an unusually long hinge extending nearly the length of the shell, and by the marked shallowness of the subauricular sinuses. The holotype has a height of 14 mm.; length, 13 mm.; hinge length, 12 mm. There are five or six costae on the rear auricle extending. from the apex of the shell across the posterior auricle. There are light costae on the anterior auricle, half of which are second order intercalaries, The anterior auricular sulcus is quite smooth with no trace of costae. About 46 costae occur on the shell body in at least two and probably three orders. The umbonal angle is about 80 degrees.

Comparison—There is no other described species that combines the small size and shallow marginal sinuses of this form. Inasmuch as it is quite rare, nothing is known of the variability of the species.

Material—Through the generosity of Dr. J. Marvin Weller, I have had an opportunity to examine the holotype (Illinois Univ., No. 10,931) and. a paratype (Illinois State Mus., No. 3,009). The paratype is apparently distorted and is too poorly preserved to be used in describing the species. Both specimens are somewhat crushed and do not retain any of the shell except traces of the outer ostracum.

Occurrence—Upper Carboniferous. The holotype was collected from a soft, argillaceous, dark-gray shale in Adams county, Illinois, in beds of Des Moines age. According to Dr. Harold Wanless (personal communication),

the marine section in Adams county, Illinois, includes several horizons. The highest of these would be slightly below the Pawnee limestone (of the northern Mid-Continent) and the lowest would. probably be above the Tebo coal equivalent. I believe the latter horizon is more likely to have yielded this species, though I may be mistaken.

In the collections before me there is a single specimen from the Willard shale (Wabaunsee) at Nebraska City, Neb., that is remarkably like A. coxanus. My hesitancy in classing the Willard form as coxanus is based on the great age difference between the two, and the fact that I cannot be sure, in the absence of other specimens from the Willard shale, that my one specimen is a normal adult.


Plate 4, figures 19-22

Aviculopecten mazonensis Worthen, 1890, Illinois Geol. Survey, vol. 8, p. 117, pl. 22, fig. 9.

Moderate sized slightly prosocline aviculopeetens characterized by a dorsoventral arching of the plane of the left valve indicative of a marked anterior and posterior gape; number of costae on shell body and auricles rather high; costae either narrow and separated by spaces as broad as the costae or relatively broad and closely spaced; umbonal angle rather large for the genus, ranging between 85 and 95 degrees in mature specimens; full-sized individuals commonly longer than high; immature ones higher than long. The umbonal folds and auricular sulci ill-defined, the anterior ones being somewhat more distinct than the posterior ones; surface entirely devoid of spines or projecting imbrications but ornamented throughout by unusually distinct, fine fila, 10 to 20 occurring in one millimeter; extraordinary in having a prismatic outer ostracum in both valves with the individual polygonal prisms separated rather widely by a matrix of what must have been originally conchiolin; prisms of the same order of size in both valves increasing in size with maturity. In one left valve the prisms along a middorsoventral line measured 20 microns at a shell height of 3 mm., and 35 microns in diameter at a shell height of 11 mm. The convexity is moderate, of the same order as in similar species.

Measurements of specimens of Aviculopecten mazonensis are given in the table previous.

Comparison—This species scarcely can be confused with other similar forms. The more striking features are the persistent prosocline obliquity, anterior and posterior shell gape, flatness of the umbonal folds and auricular sulci, and the high costal count. The shell structure and breadth of cardinal area are distinctive features, although these characters are less easily observed.

Material—Through the courtesy of Dr. J. Marvin Weller and the Illinois State Museum, I have studied the holotype and a topo-paratype (Illinois State Mus., No. 2592), and a topotype (Illinois State Mus., No. 13,190). In the collections of Yale University, Peabody Mus., there are 12 topotypes of the species (Nos. 14,454-14,458). The specimens are all preserved alike, being more or less distorted and crushed. Except for an outer ostracum and traces of a periostracum, the shell substance is altered or lacking.

Occurrence—Upper Carboniferous. The specimens occur in silty ironstone concretions associated with the famous brackish water and terrestrial fauna and flora of the Mazon Creek beds (Des Moines age), Mazon Creek, Grundy county, Illinois. Doctor Harold Wanless writes me that "these shales, with their famous fossil plants, probably belong slightly above your Tebo coal" (of the northern Mid-Continent).


Plate 5, figure 3

Aviculopecten mccoyi Meek and Hayden, 1864, Paleontology Upper Missouri, p. 50, pl. 2, fig. 9.

The holotype is a rather small, acline left valve in which the costae rapidly increase in size during growth so that there is a very pronounced differentiation in size between alternate costae on the marginal part of the shell. On the posterior auricle there are 8 distinct costae on the dorsal half of the auricle and 9 crowded fine ones on the ventral half, making 17 in all. There are 42 costae on the shell body, of which 8 or 9 are conspicuously larger, particularly those on the middle part of the shell, and have vaulted imbrications or spine bases at irregular widely spaced intervals. The first order costae are separated by 3 or 7 smaller costae on the shell body which are introduced quite regularly. There are 9 costae on the anterior auricle, 4 of which are of the first order, the others second order. Imbricating growth near the shell margin suggests that the holotype is a full sized individual. There are traces of very fine fila on the less worn parts of the shell, about 50 occupying the space of 1 mm. near the ventral margin. The height of the holotype is 22 mm.; length, 19 mm.; hinge length, 14 mm.; umbonal angle, 85 degrees; convexity, about 5 mm.

Comparison—Unfortunately, this species was founded on insufficient material so that the range of variability is not known. Until authentic topotypes can be obtained better to establish the characters of the species, the relative importance of the features shown by the holotype cannot be definitely established. The features which especially distinguish the holotype are the rapidly expanding spinose costae.

Material—A single specimen, the holotype, is kept at the U. S. Nat. Mus. (No. 2,521) where I was permitted to study it by the curators of that institution. The shell is fairly well preserved, retaining most of the original shell substance.

Occurrence—Permian. The holotype occurs in a light-gray to white oolite matrix in which there are many molds of shells. It is said to have been obtained from South Cottonwood Creek, Kansas. The horizon is probably near the Fort Riley limestone of Lower Permian age.


Plate 5, figures 8-10

Aviculopecten vanvleeti Beede, 1902, Oklahoma Geological Survey, Advance Bull., First Bien. Rept. p. 6, pl. 1, figs, 8-86; 1907, Kansas Univ. Sci. Bull., vol. 4, p. 159, pl. 5, figs. 2-2e.
Aviculopecten oklahomaensis Beede, 1907, Kansas Univ. Sci. Bull., vol. 4, p. 158, pl. 5, figs. 3-3c; pl. 6, figs. 11-11c.

Shell of moderate size, higher than long, variable in form and obliquity from slightly prosocline to slightly opisthocline; posterior auricle slightly shorter and distinctly smaller than the anterior one; beak of left valve small, narrow and extended slightly above the hinge; umbonal angle small; posterior umbonal fold poorly defined, although there is a rather sharply defined sulcus at the inner margin of the rear auricle setting it off from the highly convex umbo; anterior umbonal fold and sulcus well defined and nearly straight in most of the specimens; an obscure radial sulcus or flattening occurs just within the posterior margin of the left valve recalling a similar but more pronounced feature in Pseudomonotis; from three to five of the first order costae across the middle of the shell body in many specimens are very much coarser than the others and have a knobby appearance where spines or projecting imbrications formerly occurred; the marginal costae of the shell body are not particularly coarse; spaces between coarse costae occupied by 6 to 10 closely spaced fine subequal costae; auricles covered with fine, subequal costae; hinge as in Aviculopecten.

Measurements of specimens of Aviculopecten uanoleeti are given in the table previous.

Comparison—This striking form is not very like any other species with which I am familiar. The ornamentation is similar to A. girtyi, but the narrow beaks, great height, small posterior auricle, and posterior sulcus on the shell body readily distinguishes the present form. A. vanvleeti is an Aviculopecten, but it is certainly a nontypical one. The species A. oklahomaensis Beede is included in the synonymy of A. vanvleeti in which the ornamentation is poorly preserved and consequently indistinct. However, the first order costae in some of the types of A. oklahomaensis were actually finer than in A. vanvleeti and in some of the specimens the body costae are nearly uniform in size. The circumstance that all of the type specimens of the two species were found together, and the fact that there appears to be a gradation from forms having a few very large first order costae to those having little or no differentiation of costae into coarse and fine ones, suggests that only one species is involved.

Material—The holotype of A. vanvleeti is destroyed. In the original publication of the species Beede (1902, p. 11) designated his figure 8 of plate I as the type and this specimen was subsequently destroyed (see Beede 1907, p. 142). There are three metatypes (Kansas Univ., Paleont, Type Coll., No. 363) left valves, that are clearly conspecific with his original holotype. In addition there are nine other specimens, including the type of A. oklahomaensis, (Kansas Univ., Paleont. Type Coll., No. 363.3) all of which I regard as representatives of A. vanvleeti.

Occurrence—Permian. The specimens were found in a red calcareous sandstone composed chiefly of well-rounded and sized quartz grains. The shells are chiefly internal molds with traces of the outer ostracum preserved on one or two specimens, from Whitehorse sandstone of the Marlow formation (upper Permian), 2 miles or more southeast of Whitehorse post office, and 18 miles due west of Alva, Okla. They were taken from the top of a hill just west of the spring.


Plate 5, figure 4

Aviculopecten mccoyi White, 1877, U. S. Geol. Surveys W. l00th Mer., Rept., vol. 4, p. 149, pl. 11, fig. 2a.
Deltopecten vanvleeti Girty, 1909, U. S. Geol. Survey, Bull. 3089, p. 86, pl. 9, figs. 5, 5a.

Shell rather large, having an estimated length and height of 35 mm. in the holotype; acline, orbicular; left valve moderately ventricose, subhemispherical, with large subequal auricles; umbonal folds nearly straight, the anterior one being particularly prominent and curved outward almost imperceptibly; anterior sulcus deep and broad, posterior one shallow, and narrow with its axis quite close to the body of the shell; shell body ornamented by costae of three distinct sizes corresponding to the oldest three ranks of costae, later costae are scarcely differentiated; there are on the holotype about 65 costae on the body of the shell of which 5 are quite coarse, 5 are intermediate in size, and the remaining ones are very fine and closely spaced, generally 6 of the finer ones separating the coarse first order costae from the second order; about 9 costae occur on the dorsal part of the anterior auricle and the anterior sulcus appears to be ornamented with much more obscure costae; posterior auricles with at least 8 small costae; umbonal angle 87 degrees; convexity about 7 mm.; hinge length, about 27 mm.

Comparison—I have no hesitation in classing Girty's Deltopecten vanvleeti from the Manzano group of New Mexico with this species. Girty (1909, p. 86) speaks of "fine concentric, lamellose lines which tend to form scalelike spines upon the costae, the size and frequency of the costae bearing a direct relationship to the size of the costae themselves. Those upon the large primary ribs are large, producing nodes upon them, and they are a long distance apart." The single specimen on which A. girtyi is founded is not sufficiently well preserved to exhibit these details of concentric ornamentation. Aviculopecten girtyi differs from A. vanvleeti in the extended posterior auricles. Furthermore, A. vanvleeti has a markedly higher form, whereas A. girtyi is more nearly subcircular. Aviculopecten kaibabensis is similar to A. girtyi, but is distinguished by a large number of subequal costae, whereas A. girtyi exhibits a marked differentiation of coarse and fine costae.

Material—The holotype (Texas Univ., No. 12,310) is an incomplete left valve exhibiting very well the general character of form and ornamentation. The shell substance appears to be completely altered.

Occurrence—Permian. The holotype was found in a gray, highly calcareous quartz sandstone, in which the separate grains are rather well rounded. This rock belongs in the middle Permian Word formation, Glass Mountains, West Texas, about 1.5 miles north 55° west of the old Hess Ranch House. Other material, described by Girty, was collected from the Permian Manzano group of New Mexico. The species is doubtfully identified in the Kaibab limestone (Permian), lower Kanab canyon, Arizona.


Plate 5, figures 11a, b

This extraordinary form bears a striking resemblance to some of the Ostreidae or Pseudomonotis, but it is certainly a member of Aviculopectinidae. The shell is acline, with subequal auricles and deeply impressed auricular sulci, both of which curve outward slightly and equally. Well-defined umbonal folds are lacking because of the uniform and low convexity of the umbonal slopes. The remarkably convex beak is acute and narrow, extending distinctly above the hinge. A striking sulcus extends from beak to shell margin along the posterior part of the shell body, producing a posterior lobation like that of Pseudomonotis and most Ostreidae. The ornamentation consists of 9 or 10 coarse first order costae separated by conspicuously smaller costae of two or three higher orders.

Measurements of Aviculopecten gryphus are given in the table previous.

Comparison—This species is like A. vanvleeti Beede in having a narrow, projecting beak. It may be readily distinguished from the latter by the very deep and curved auricular sulci, greater convexity, larger posterior auricle, and more numerous coarse first order costae. Furthermore, the anomalous posterior sulcus of the shell body is very much more pronounced in A. gryphus than in A. vanvleeti. The form of the auricles and character of the ornamentation in A. gryphus are typical for Aviculopecten. The extraordinary production of the beak, and the posterior sulcus of the shell body, together with the rather high convexity, suggests some genus like Pseudomonotis. Pseudomonotis is especially distinguished by the absence of an extended posterior auricle, which in the present species is acute and fully developed.

Material—The species is based on a dozen fragmentary specimens, all of which belong to left valves (Texas Univ., No. 12,311). The preservation is not good; consequently further details of the finer ornamentation may be discovered when better material is collected.

Occurrence—Middle Permian. The types occur in a gray matrix of hard siliceous limestone with fragments of brachiopods and fusulinids, Word formation, Glass Mountains, West Texas, 1.5 miles north 55° west of the old Hess Ranch House.


Plate 5, figures 1, 2

Aviculopecten coreyana White, 1874, U. S. Geog. Surveys W. l00th Mer., Prelim. Rept. Invertebrate Fossils, p. 21.
Aviculopecten coreyanus White, 1877, U. S. Geog. Surveys W. 100th Mer., Rept., vol. 4, p. 147, p. 11, figs. 2a, 6.
Deltopecten coreyanus Girty, 1909, U. S. Geol. Survey, Bull. 389, p. 87.

Shell large, acline, orbicular, with an extraordinarily long hinge margin for an Aviculopecten; umbonal slopes, particularly the posterior one, poorly defined; anterior sulcus well differentiated, but the posterior one broad and shallow, with its axis near the middle of the auricle; shell surface of the left valve ornamented by a large number of intercalate, closely spaced costae, about 65 occurring on the shell body, 8 to 12 on the anterior auricle and somewhat less on the posterior auricle; umbonal angle in the type specimens about 85 degrees. Regarding the right valve, specimens of which are lacking in the type collection, Girty (1909, p. 88) says, "This is considerably less convex than the left, but by no means entirely flat. It has almost the same shape as the other, the byssal sinus being not as deep as in some species. The surface, I am inclined to believe, is destitute of any radial markings but crossed by fine lines of growth, some of which are sublamellose." Girty (1909, p. 88) was also able to examine the hinge of some specimens of A. coreyanus from the Permian Manzano group of New Mexico. "D. coreyanus proves to have a broad beveled cardinal area, with triangular cartilage pit beneath the beaks."

Comparison—This species recalls some of the elongate Pterinopectinidae in the great shell extension below the auricles. However, Girty's observation on the hinge characters of the species indicate that it is in reality one of the aviculopectinids. I have not seen a right valve of the species, but if the right valve is truly devoid of any radial ornamentation, the species cannot be a true Aviculopecten.

Occurrence—Permian, Manzano group, New Mexico. The types (U. S. Nat. Mus., No. 8,522) are said to have been collected 1 mile south of Pajuate, N. M., east of Mount Taylor.


Plate 5, figures 5, 6

Aviculopecten halensis Mather, 1915, Denison Univ., Sci. Lab. Bull., vol. 18, p. 223, pl. 15, fig. 17.
Aviculopecten arkansanus Mather, 1915, Denison Univ., Sci. Lab., Bull., vol. 18, p. 226, pl. 15, fig. 13.

This species is known from very small gibbous left valves, which, because of their small size, inflation, and a very marked yet fine filose ornamentation, resemble somewhat the juveniles of other species, and, indeed, lacking sufficient material, it is not easy to prove that they are not juveniles. The flaring curvature of the anterior umbonal slope, however, suggests that the types are approaching maturity. These shells appear to be acline and are ornamented with narrow high costae arranged in three ranks, separated by interspaces three to four times their own width. The posterior body costae is no larger than the other first order costae so that the posterior umbonal fold is rather obscure and broad. The costae are capped by imbricating scales produced where fine fila cross them. Costae are almost completely absent along the inner part of the anterior sulcus.

Through the courtesy of Dr. Carey Corneis of the University of Chicago, I have been able to compare directly the types of A. arkansanus and A. halensis, and it seems probable that they belong to the same species.

The holotype of A. arkansanus Mather, Walker Museum, Univ. Chicago (No. 16,053), is a nearly complete left valve with the outer surface imbedded in a matrix of dark-gray oolitic limestone. It was implied from Mather's description, and stated by Price (1916, p. 720), that this specimen is an external mold. This interpretation is incorrect as even a cursory examination of the specimen under xylol shows. The valve is truly a plicate one, and the original inner surface retaining the hinge is intact. An examination of the ventral margin shows that the outer ornamentation consists of at least two orders of distant, elevated costae. With the aid of xylol 20 body costae, of which at least 9 are intercalaries, can be seen. At least 4 costae on the anterior auricle and 5 on the posterior one are visible through the shell. There is a well-defined cardinal area, like that of other aviculopectens, and the margin of a resilifer can be seen at the middle of the exposed part of the area. The specimen was found in the Hale formation, East Mountain, Fayetteville, Ark., at nearly the same horizon as the types of A. halensis. Although it cannot be proved that A. arkansanus is synonymous with A. halensis, it seems quite likely that the two are the same.

Measurements of specimens of Aviculopecten halensis are given in the table previous.

ComparisonAviculopecten halensis Mather is distinguished especially by the combination of the following characters: number and character of the costae, the imbricating scales of the costae, number of anterior costae, ill-defined posterior umbonal slope, absence of costae on the inner part of the anterior auricular sulcus, and the small size of the shell. The larger number of costae and greater umbonal angle distinguishes this species from the similar A. eacleneis (Price).

Material—The types of A. halensis Mather (Walker Museum, Univ. Chicago, No. 16,051) consist of six fragmentary specimens, external molds of left valves, in a silty, black and gray, noncalcareous shale, associated with molds of Bryozoa.

Occurrence—Upper Carboniferous. Hale formation, Morrow subseries, East Mountain, Fayetteville, Ark.


Plate 11, figures 1-4

Deltopecten flabellum Price, 1916, West Virginia Geol. Survey, Rept. on Raleigh, Mercer, and Summers counties, p. 720, pl. 31, figs. 3-6.

Shell rather small for the genus, acline or only slightly prosocline, suborbicular, slightly longer than high; anterior auricle quadrate or acute, sharply depressed below the shell body, set off by a narrow sulcus in which there are rarely any transitional costae; posterior auricle poorly differentiated from the shell body by a shallow and broad sulcus which nearly covers the entire auricle; outer margins of each auricle indented in a broad, shallow sinus; surface ornamented with broad costae, closely spaced, which increase by implantation on the left valve, by bifurcation on the right; crossed by obscure fine fila spaced up to 0.1 mm. apart; costae on shell body tend to be coarser across the middle area, progressively become weaker toward the front and rear margins of the shell, and curve slightly outward from a mid-line of either valve; anterior auricle generally with two to four costae, posterior one possessing up to three. There is a well-defined cardinal costa on either auricle.

Measurements of Aviculopecten flabellum are given in the table previous.

Comparison—This species has the general expression of a Dunbarella, but differs in the extended and acute rear auricle and in possessing filose ornamentation on the better preserved shells. Since the hinge structures are unknown, this species may conceivably belong with the Pterinopectinidae.

The salient features that most readily distinguish this species from similar aviculopectens are: the angular anterior auricle of the left valve, coarse costae, and the elongate form of the shell.

Material—The figured types of this species could not be located, but through the generosity of Mr. Dana Wells at West Virginia University, I have had an opportunity to study 30 of the syntypes of the species. The types are at West Virginia Univ., Coll. Nos. 507, 509, 638, 634, 637, 635 and 636. They are for the most part poorly preserved molds of the inner surface of the outer ostracum layer. A few specimens retain part of the outer ostracum, but in no instance is there any trace of the inner ostracum. Several localities and horizons are represented in the collection.

Occurrence—Upper Carboniferous. Kanawha group, upper Pottsville, roof shale of the Little Eagle Coal, hillside northwest of Oceana, and along Cedar Creek of the Clear Fork of the Guyandot, Wyoming county, West Virginia; Cannelton limestone, roof of the Matewan coal, Kanawha group, Huff Creek, 0.5 mile north of the mouth of Laurel Branch, 1.4 miles south of the corner of Wyoming, Logan, and Boone counties, West Virginia. The specimens occur in a matrix of light- to dark-gray silty shale somewhat carbonaceous.


Plate 4, figures 17, 18

This is a robust orbicular Aviculopecten, easily distinguished from other North American species. The individuals attain a relatively large size with a maximum height and length of at least 60 mm. The convexity is quite marked, so that mature left valves are subhemispherical. The right valve is unknown. In addition to the large size, the species, unlike most aviculopectens, is characterized by an almost complete absence of a posterior umbonal fold. The ornamentation is characteristic, consisting of a relatively large number of moderately coarse, closely spaced costae, numbering at least 85 on the shell body of a specimen having a height of 60 mm. The anterior umbonal fold is only slightly curved outwardly so that the umbonal angle is only moderately flaring. Both auricles are costate, but the anterior one is poorly shown in the material at hand. The posterior auricle is ornamented differently from the shell body, and the juncture of the posterior auricle with the shell body defines the rear margin of the umbonal angle. The costae on the rear auricle, numbering 12 or 15, are widely spaced and relatively narrower than those on the general shell surface.

Measurements for the holotype
Height 60 mm
Length 60 mm
Umbonal angle 91 degrees
Convexity 13 mm
Body costae 85

Material—The species is based on three specimens, including the holotype, all from a single locality. Types, Kansas Univ. Paleont. Type Coll., Nos. 361.1, 361.2.

Occurrence—Permian, upper part of the Kaibab limestone in yellowish, porous dolomitic limestone associated with innumerable molds of other mollusks, (Bellerophon beds), Padre Canyon, on main highway east of Flagstaff, Ariz.


Plate 5, figure 16

This species is very like A. gradicosta and, indeed, probably is a descendent of the Pennsylvanian form. Although there is only a single specimen, a left valve, of the new species at hand, its characters are such that it can be readily recognized. It differs from A. gradicosta in the greater number of costae at a comparable growth stage. At a height of 22 mm. there are 93 costae of which 6 are transitional on the anterior umbonal fold, whereas in A. gradricosta there are only 62 to 66. There are 8 relatively coarse first order costae which are coarsely spinose, separated by 14 or 15 finer costae in two orders. The holotype has a height of about 25 mm., length about 23, and a hinge length of around 22 mm. There are 9 distinct. costae on the posterior auricle and at least 11 on the incomplete anterior auricle. The umbonal folds are nearly straight and diverge at 80 degrees. The convexity ratio is about 0.20.

Material—This beautiful little species is based on a good external mold of a left valve. The holotype is Kansas Univ. Paleont. Type Coll., No. 364.

Occurrence—Permian, upper part of Kaibab limestone in brown dolomitic limestone, filled with molds of shells, chiefly mollusks, (Bellerophon beds), Padre canyon, at highway east of Flagstaff, Ariz.


Plate 6, figures 17, 18

A robust Aviculopecten is common in the Summer group of the Big Blue series in Kansas. For a time, I was disposed to class this form with Aviculopecten basilicus, n. sp., which it closely resembles. There are a few specimens associated with typical representatives of the new species which could not be readily distinguished from A. basilicus, and I am open to criticism in establishing two new names for forms which many discriminating paleontologists would prefer to class as a single species. Aviculopecten basilicus is found several hundred feet below A. sumnerensis, in the Douglas group, and similar forms have not been found in the intervening Shawnee and Wabaunsee groups. A dozen specimens of A. sumnerensis from the Sumner group could be distinguished from a like number of specimens of A. basilicus from the Douglas group.

Superficially the two forms are exceedingly alike. Both are relatively large and robust, commonly having a height and length of about 40 mm.

Measurements of specimens of A. sumnerensis are given in the table previous.

In most of the left valves of A. sumnerensis there are but 8 or 9 costae visible on the front auricle, whereas there are generally 11 on specimens of A. basilicus. This distinction is not emphasized here, however, because all of the specimens of A. sumnerensis are sub internal molds and the ornamentation is correspondingly weak so that costae cannot accurately be counted. Many of the specimens of left valves show incipient bifurcation of the coarser costae at a height of more than 30 mm., but this habit is not constant and there are many specimens in which there is no trace of such bifurcation.

The chief character by which good collections of A. sumnerensis can be distinguished from A. basilicus is the size of the umbonal angle. In my specimens of A. basilicus a maximum of 90 degrees was measured, whereas an angle of more than 95 degrees was measured in a number of specimens of A. sumnerensis. It seems proper that the average size of the umbonal angle should be greatest in those specimens which are geologically youngest because during the ontogenetic change of any Aviculopecten, there is a continuous increase or flare in the umbonal angle reaching a maximum at maturity.

Through the generosity of the Texas Bureau of Economic Geology, I have before me five fragmentary specimens of a large Aviculopecten that I am tentatively identifying with A. sumnerensis. The specimens are labeled Limipecten n. sp. Beede, 1909. These specimens came from limestone quarries in the Arroyo formation at Ballinger, Runnels county, Texas. These specimens were at first regarded as topotypes of Aviculopecten ballingerana Beede, the primary types of which are lost. Unfortunately, Beede's specimens were never illustrated. He sought to distinguish his species by a marked bifurcation of the costae of the left valve. The material at hand from Ballinger is well enough preserved to show that none of the costae of the left valves bifurcate. There are no specimens of A. summerensis before me in which the bifurcation is at all marked, and partly for that reason, in addition to the fact that too little is known of Beede's species, I have deemed it unwise to revive the term ballingerana when there is no assurance that the original types were even members of Aviculopecten s. s.

Material—The species is based on a large number of subinternal molds, chiefly from one horizon, the Herington limestone. Holotype, Kansas Univ. Paleont. Type Coll., No. 371.1.

Occurrence—Lower Permian. Common in the Herington limestone (Big Blue series) in Kansas and Nebraska. The holotype was found by M. K. Elias at this horizon 1 1/2 miles southeast of Spence siding, Washington county, Kansas. Other specimens were found in the Arroyo (lower Permian) formation at Ballinger, Tex. (Texas Bur. Econ. Geology, No. 9,876), and in the Krider, Burr, and Fort Riley limestone, and doubtfully from the Florena shale, all from the lower Permian Big Blue series.


Plate 6, figures 11-12b

There is no form to my knowledge that might be confused with this unorthodox Aviculopecten. It is remarkable in having an extraordinarily convex left valve when viewed dorsally, whereas the right valve is markedly concave when viewed dorsally or ventrally. There is no other Aviculopecten that has a concave right valve, but I have no hesitancy in assigning this form to the genus. Although the specimens at hand are internal and subinternal molds, there are low prominences marking the former site of rather coarse spines that originated from the larger costae. The posterior umbonal slope is so ill-defined that a measurement of the umbonal angle is impracticable. There is no evidence of costae on the rear right and left auricles. Owing to poor preservation, a precise count of the body costae is difficult, but in several specimens the count ranges between 40 and 50 for specimens having a height of around 3 to 4 cm. The ligament area is relatively broad, having a breadth of nearly 2 mm. in one specimen having a hinge length of about 23 mm.

Material— The species is based on nearly a score of specimens, all internal or subinternal molds, and all from one horizon, but representing several localities in northern Kansas. The holotype, (Kansas Univ. Paleont. Type Coll., No. 368.1), as well as most of the paratypes, come from the Fort Riley limestone 1 mile east of Marysville, Kan.

Comparison—There is no other Aviculopecten with which this form may be confused. The high antero-posterior convexity of the left valve, and corresponding convexity of the right valve, are distinctive.

Occurrence—Lower Permian. Buff, dolomitic limestone, filled with molds of shells chiefly mollusks, Fort Riley limestone, Big Blue series, Kansas.

Genus LIMATULINA De Koninck, 1885

Limatulina De Koninck, 1885, Faune des Cal caire Carbonifère de la Belgique, Lamellibranches, p. 243.
Genolectotype, Limatulina radula (De Koninck), Viséan, Belgium.

Original diagnosis: Coquille inéquivalve, obliquernent ovale, plus haute que longue; valve droite un peu moins convexe et un peu plus petite que la gauche; crochets distants, faiblement bombés séparés par une aréa occupant toute la longueur du bord cardinal; oreillettes antérieures petites, nettement définies: celie de la valve gauche plus ou moins renflée, tandis que celie de la valve droite est plane et accompagnée d'une fente étroite destinée au passage du byssus; Ie restant des bords libres des valves hermétiquement clos; surface garnie de côtes rayonnantes plus or moins épaisses, ordinairement rugueuses ou traversées par des plis concentriques formant avec elles un réseau plus ou moins régulier.

A genotype was not selected by De Koninck, nor, as far as I can learn, by later writers. The genosyntypes were Limatulina etheridgei De Koninck, L. selecia De Koninck, L. linguata De Koninck, L. heberti De Koninck, L. radula De Koninck, and L. loricata De Koninck. It does not appear to me that all of these shells are congeneric, even allowing for De Koninck's unsatisfactory descriptions and misleading illustrations. It has not been possible for me to examine authentic specimens of anyone of these species. One species, L. radula, resembles the juvenile stage of Aviculopecten, and, according to De Koninck's description, the type of this species possesses intercalate costae on the left valve and bifurcate costae on the right valve. He described the ligament area as being smooth, so, in all probability, it is one of the Aviculopectinidae. Highly probable, also, is the conclusion that L. radula is a true Aviculopecten, whereas some of the other species most certainly are not. I propose here to designate L. radula (De Koninck) (see fig. 9, pl. 7) as the genolectotype of Limatulina, thus placing a poorly known and troublesome genus in synonymy with Aviculopecten. When De Koninck's material is critically restudied, it may develop that L. radula is not an Aviculopecten, but at the present time it appears to me very probable that L. radula was based on juveniles of some larger species of Aviculopecten.

Genus DELTOPECTEN Etheridge, Jr., 1892

Plate 8, figures 6a-d

Deltopecten Etheridge, Jr., 1892, in Jack and Etheridge, Jr., Geology and Palaeontology of Queensland and New Guinea, p. 269.
Genotype, Pecten illawarensis Morris, Permian, New South Wales, Australia.

Original diagnosis: Shell possessing the general structure of Aviculopecten, but the valves are very inequivalve, the larger or convex valve with a high overcurved umbo, overhanging a long triangular hinge area, with longitudinal cartilage furrows, and a large deltoid-triangular cartilage pit.

The term Deltopecten has come to be applied in recent years, incorrectly I believe, to a large proportion of the Carboniferous Pectinacea. For the past 80 years, following McCoy'S diagnosis of Aviculopecten, paleontologists have thought that Aviculopecten is characterized by the presence in each valve of a smooth, flat, ligament area devoid of a resilifer. No such structure is known in any of the modern Pectinacea or Pteriacea, nor in any other modern or fossil group. Confusion was added when James Hall amended the original diagnosis to include pectinoid forms with or without resilifers or having a grooved ligament area. According to Hall's interpretation, the genus Aviculopecten. was classified largely on the basis of form and ornamentation, with no regard to the cardinal structures. The presence of a median resilifer in an aviculopectinid shell was regarded as such a novelty, even 40 years after McCoy's diagnosis, that Etheridge was impelled to erect the genus Deltopecten, distinguished mainly by having a large median resilifer below each beak. As early as 1866, Meek (Meek and Worthen, 1866, p. 331) had noted a similar hinge arrangement in Aviculopecten occidentalis (Shumard), but he had placed no particular importance on his discovery, and, consequently, it did not become generally known. In 1904, Girty (p. 721) described some exceptional specimens from Texas showing a broad, smooth ligament area and central resilifer, He based the new genus Limipecten on these specimens, supposing it to be distinguished from Aviculopecten by the presence of the resilifers. On learning that Deltopecten previously had been erected on the same basis, he abandoned Limipecten and referred many of the Carboniferous and Permian species of pectinoids to Deltopecten.

As a result of the present investigation, it has developed that all of the true aviculopectens, including many quite diverse shells, have a shallow central resilifer, similar to that of modern Lima or Pinctada. Obviously, other characters than the mere presence or absence of resilifers are needed to differentiate the Paleozoic pectinoids.

No reasonable effort has been spared in attempting to learn the exact characters of Deltopecten. Yet, in absence of specimens of the genotype species, some of the significant features still remain unknown. Through the generous cooperation of the curators at the British Museum, I have been enabled to study excellent casts (see pl. 8, figs. 6a-d) of the holotype of Pecten illawarensis Morris. A restudy of the type specimen seemed important because Etheridge (Etheridge and Dun, 1906, p. 25) himself was not sure of his identification of the species on which he based Deltopecten: The type specimen shows that the shell was extraordinary in being truly plicate, having a few large, simple, rounded plications that normally do not increase in number during growth. The ornamentation is nearly alike on both valves, and the plications interlocking at the margin, as in many modern Pectinidae. No American Carboniferous shell of my acquaintance has this kind of ornamentation. Another feature, not shown by the fragmentary holotype, but one which seems to exist in many of the Australian pectinoids, is the coarse linear ligament furrows that occur on the ligament area of each valve. It seems curious that several of the Australian shells with diverse ornamentation have been described as having ligament grooves in addition to resilifers. It is futile to speculate on these characters until detailed descriptions and figures are available to show the ligament area in several of the species, especially Deltopecten illawarensis, or one of the other species having simple plications.

Dr. Leslie Bairstow, of the British Museum, has generously supplied the following observations on the type specimen of Deltopecten illawarensis (Morris) :

We have the type specimen of Pecten illawarensis Morris, registered No. 96,893. The two valves are in appositiorn. The specimen is incomplete, as represented in pl. XIV, Fig. 3, of Morris in Strzelecki; being truncated where it reaches the eroded surface of the containing rock. The specimen is in three portions: an internal mold, with some flakes of shell adherent to it, and two counterparts, with much of the flaky lamellar shell adherent to them. pl. XIV, Fig. 3, represents the internal mold, together with the pair of apposed ears, which are both adherent to one of the counterparts, and not attached to the internal cast. Most of the hinge-line is missing, only the one ear of each valve being preserved; and as these two ears are in apposition, their internal surfaces are concealed.
The ribs are folds of the shell, and show strongly both on internal and external molds. To a first approximation, the number of ribs remains constant through the successive growth stages, from a very early stage. In the later growth layers, some of the ribs come to have flattened crests; and further, in one or two cases, it faint longitudinal hollow develops along this flattening, suggesting incipient bifurcation. The two or three ribs that start in closest proximity to the preserved ear of each valve are undulations of smaller amplitude than that of the other ribs visible, and one or two of these "lateral" ribs seem to have arisen by intercalation. Judging from those parts of the external molds that are free from flakes of shell, the external surface of the shell shows the growth layers, and (scarcely visible to the unaided eye) a finely granular pattern resembling engineturning. The internal mold is smooth and polished.
The matrix of the counterparts contains portions of two other valves of Pecten, apparently of the same species; but neither of these is more completely preserved than the type specimen.
As so much, e. g. of the hinge-line, is missing, the typespecimen of Pecten illawarensis, taken alone, does not exhibit all the characters required for a complete diagnosis of Deltopecten. But, in my opinion (for what it is worth—I have not worked on lamellibranchs), if further material could be obtained from the type locality, it should be possible to decide its identity or otherwise with the typespecimen of P. illawarensis, which seems fairly distinctive.
The only provenance-information on the original label with the specimen is "Illawara." The matrix is a reddish-brown to grey, slightly micaceous, finely granular, impure limestone, with some still finer textured inclusions. The Pecten shells are of flaky calcite, colour variable from white to yellowish-brown and brown. In the matrix of one counterpart there is a minute gastropod.

Several large pectinoids from the Permian of southeastern Australia occur in the Dana collection at the U. S. National Museum. Although these forms all fall in the genus Deltopecten. as generally employed, I believe that they represent several genera, because they display several fundamentally different types of ornamentation.

Some of the National Museum specimens exhibit striated or deeply grooved ligament areas. In order to learn whether or not these grooves are chevron grooves, comparable to those of Arca, or are merely irregular varices of growth, I appealed to Mr. F. Stearns MacNeil of the U. S. Geological Survey. Mr. MacNeil has communicated this opinion:

In the forms you inquired about the grooves on either side of the chondrophore are not ligament grooves. The chondrophore is very large and slightly oblique, and the grooves, although not exactly horizontal, are clearly growth lines—or rather, say, the eroded edges of successively deposited layers.

As far as I can learn, Deltopecten s. s. is restricted to Middle and Upper Permian rocks of the eastern hemisphere. In addition to the genotype D. iliawarensis (Morris), Aviculopecten mitchelli Etheridge and Dun, and A. squamuliferus Morris, from the Middle Permian of Australia, are representatives of Deltopecten. The Upper Permian species, Aviculopecten jabiensis Waagen, A. derajatensis Waagen, A. subexoticus Waagen, and A. pseudoctenostreon Waagen, from the Salt Range of India, are representatives of Deltopecten.

Probably Deltopecten had its origin during the Pennsylvanian or Early Permian in Acanthopecten, the only other Paleozoic pectinoid thus far recognized that has a constant number of costae during growth.

Genus FASCICULICONCHA Newell, n. gen.

Acline, truly pectiniform, symmetrical shells characterized by having the intercalate costae of the adult left valve arranged in fascicles that are separated by broad, generally smooth mterspaces, rarely having faint costellae within them. Costae commonly arranged in three ranks, less commonly four, of which the first two are like those in Aviculopecten, showing no tendency towards fasciculation; third and fourth series introduced by intercalation in close position to the older series, producing the bundling characteristic of the genus. Auricles ornamented by fine, widely spaced non fascicled costae which increase by intercalation; auricle sulci broad, shallow, with axis close to the shell body. Umbonal folds subangular, narrow, prominent. Surface of shell body covered with fine, somewhat irregular fila which generally lose their distinctness on the auricles and over the adult part of the shell; these fila produce small projecting imbrications where they cross the costae. Musculature apparently like that of Aviculopecten. Resilifers similar to that of Aviculopecten; but differing slightly in the shape of its front margin, which diverges outward from the beak until an intermediate growth stage is reached; then the margin is recurved posteriorly so that the anterior termination of the resilifer is a rounded V-shaped margin, midway between the dorsal and ventral edges of the ligament area. There is a very marked dorsoventral curvature of the shell margin in the type species, which is suggestive of either a pronounced anterior and posterior gape. Right valve ornamented similarly to Limipecten, with relatively fine costae which increase in number during ontogeny by implantation of new costae at the shell margin. Shell micro-structure like that of Limipecten, from which the genus apparently was derived.

Genotype—Fasciculiconcha knighti Newell, n. sp.

Range—Des Moines to lower Virgil subseries, Upper Carboniferous (Pennsylvanian series).

Measurements of Specimens in Species of Fasciculiconcha
Species Specimen Length,
Auricular costae No.
No. body
Anterior Posterior
knighti L1 67 70 41 96± 23 12 7 23 72±
L2 60 62   90± 16   8 21 72±
L3 75 75   89± 16   10 26 87±
L4 54 57 31 85± 15.5 13 13 24 72±
L5 68 70 38 100 17 9+ 31± 100±
L6 64 61 38.5 95 16     25±  
L7 67 61 44 89 15     27±  
L8 70± 75 49 94 20 13 10 26± 109±
L9 27 29.5 19 86 6 12 8 20 59±
providencensis L1 47 44± 2.8± 94 10     30 95±
L2 48 48   90       25±  
scalaris L1 21 23 17 89 low 8 24± 56±


Plate 6, figures 19,a-c; Plate 7, figures 1-3, 5, 6; Plate 8, figure 2a, b

Aviculopecten fasciculatus Keyes, 1894, Missouri Geol. Survey, vol. 5, p. 113, pl. 42, fig. 7 (not A. fasciculatus Hall, 1883).

Orbicular large shells, about as high as wide; hinge slightly shorter than the shell length; anterior umbonal fold curved outward moderately, posterior one nearly straight, curved very slightly inward or outward but never markedly so; margin of anterior auricle rounded in a broad sinus, sigmoidally recurved at hinge; rear auricle angular, with the form of an inverted isosceles triangle, the hinge margin being slightly longer than its sides; especially characterized by a marked dorsoventral outward curvature of the valve margin, suggestive of a strong anterior and posterior gape; arching so marked in some specimens as to make them subhemispherical, with the dorsal part of the auricles curved inward at a steep angle to the plane of the valve margin; umbonal angle generally between 90 and 100 degrees, commonly 10 or 12 slender costellae with wide interspaces on the anterior auricle and 8 or 10 on the posterior auricle; axis of auricle sulci is close to the shell body, marked by smooth areas, devoid of costellae; right valve unknown.

The largest specimen known to me, a topoparatype (D. S. Nat. Mus., No. 89,092), has a length of 92 mm. and a height of 100 mm.

The species is dedicated to Dr. J. Brookes Knight. Measurements of specimens of Fasciculiconcha knighti are given in the table above.

Comparison—This species is readily distinguished by its pronounced gape, straight or nearly straight posterior fold, high convexity, and relatively broad interspaces between fascicles.

Material—The species is based on 17 fine specimens, left valves, from the Westerville oolite at Kansas City. The preservation is good, but the original shell substance appears to be altered. Holotype, Kansas Univ. Paleont. Type Coll., No. 372.1; topoparatypes, Kansas Dniv. Paleont. Type Coll., No. 372, and Yale Univ. Peabody Mus., No. 8,147, 14,466M, and U. S. Nat. Mus., Nos. 80,337, 46,377.

Occurrence—Upper Carboniferous. Westerville oolite, Kansas City region; Sniabar limestone, 1 mile south of Harrisonville, Mo.; Bethany Falls limestone, 2 miles west of Oreapolis, Neb.; Cherryvale shale, 4% miles south of Bethany, Mo.; Merriam limestone, sec. 8, T. 10 S., R. 23 E., Kan. The species is most common in the Westerville oolite, but it is nowhere abundant. One or two fragments, provisionally referred to the species, were found in the Oread limestone, but all other occurrences are in the Missouri subseries, Pennsylvanian.


Plate 7, figure 4

Aviculopecten scalaris Herrick, 1887, Denison Univ. Sci. Lab., Bull., vol. 2, p. 26, pl. 1, fig. 8.

The holotype of F. scalaris, which I have seen, appears to preserve the original surface of the shell, and there are conspicuous differences in ornamentation between this and other fasciculiconchas. The ornamentation in F. scalaris has the fascicled costae of the genus, but the regular concentric fila, so characteristic of F. providencensis, are lacking in this shell. F. scalaris has a relatively low convexity, the general form of the shell suggesting Aviculopecten rather than Fasciculiconcha. I am not satisfied that the lateral costae of individual fascicles are intercalaries, as they are in other fasciculiconchas. The lateral costae appear to rise from the older ones by fission, but this cannot be determined positively from the single specimen at hand. The species Aviculopecten basilicus, n. sp. shows a tendency toward such a fission of first order costae at a late growth stage, and it is possible that a similar kind of ornamentation characterizes F. scalaris. A character shown by the holotype, probably accentuated by distortion, is an extraordinarily abrupt, narrow sulcus at the base of the anterior auricle, and the auricle rises abruptly above the depressed sulcus. A further study of this species, based on topotype specimens, is needed.

Measurements of the holotype of F. scalaris are given in the table previous.

Comparison—This species, if restricted to forms like the holotype, is characterized by a nearly straight posterior umbonal slope, and by very irregularly fascicled, apparently smooth costae. The concentric undulations, thought by Herrick to distinguish the species particularly are probably abnormalities of growth or preservation.

Material—A collection of Flint Ridge (Ohio) fossils, presented to the National Museum by the late Dr. August Foerste, contains a specimen that is almost certainly the holotype of A. scalaris. The original figure of the holotype indicates a nearly complete left valve, whereas the present specimen is broken and fragmentary, otherwise the specimen is like the figure in having the same shape and size. A label, fastened to the specimen, reads: "Plate 1, Fig. 8, Av. scalaris Herr., Bald Hill."

Occurrence—Upper Carboniferous. Lower Mercer limestone, Pottsville, at Bald Knob (formerly called Bald Hill) about 2 miles southeast of Newark, Ohio.


Plate 7, figures 7, 8; Plate 8, figures 1a, b

Pecten providencensis Cox, 1857, Geol. Rept. Kentucky, vol. 3, p. 566, pl. 8, fig. 1.

This species is similar to F. knighti but can be distinguished readily by certain distinctive characters. The posterior umbonal fold flares outward about equally with the anterior one and the costae tend to swing outward on either side of a midline; there is no marked dorsoventral arching of the shell margin, and if there was originally a shell gape, it must have been slight; increase of costae in the adult stage becomes irregular, so that the fascicles are not uniform, a fanning or spreading out of the component elements of each fascicle occurring near the margin; fine but prominent, regular fila cross both costae and interspaces on the shell; interspaces between fascicles distinctly narrower and shell size ordinarily less than in F. knighti; convexity only moderate.

This description is particularly incomplete because the specimens of this species available for the present study are all fragmentary and poorly preserved. All of the material at hand, which is from Des Moines beds, and the published descriptions of specimens of this age, appear to have the above characters. It is highly probable that better material would permit distinction of several species of Des Moines age, but all can be distinguished readily from younger forms by the above characters. Cox's type is lost, but its locality and exact horizon (Allegheny) are known, so that topotypes may be secured.

Measurements of specimens of F. providencensis from Brazil, Ind., are given in the table previous.

Comparison—This species is so distinctive that it need not be confused with the other two American forms, F. knighti, n. sp., and F. scalaris (Herrick).

Material—The type of F. providencensis is lost and topotypes have not been available for the present study. Hypotypes that furnished basis for part of the above description are three poorly preserved specimens in the U. S. National Museum (No. 80,338) retaining part of the outer ostracum, and several fragmentary specimens collected from Des Moines beds at widely separated localities.

Occurrence—Upper Carboniferous. According to present information, the species is restricted to the Des Moines subseries, Pennsylvanian series. The holotype was found at Providence, Hopkins county, Kentucky, in the limestone which overlies the main coal (No. 11) at that place. This horizon belongs in the upper part of the Allegheny formation. Dr. Harold Wanless, of the University of Illinois, writes me that "this is the same as the cap of the Lexington coal (Labette shale) in western Missouri."

Material that I have seen came from Des Moines beds at the following places: Brazil, Ind. (label reads "V shale Otter"); regarding this locality Doctor Wanless reports, "I have measured a section along Otter Creek near Brazil, Ind., and there are several marine horizons. They range from the horizon of the Seville limestone up to the horizon of our Coal No.2, probably the roof of your Tebo coal." All of these are in the lower Pennsylvanian. Lower Fort Scott limestone, Fort Scott, Kan. (Kansas Univ. Paleont. Type Coll., No. 2,314); same as last, (Yale Univ., Peabody Mus., No. 14,468); upper Fort Scott limestone, near St. Louis, Mo., (Knight's loco 3, St. Louis, outlier; Pawnee limestone, east bank of Verdigris River, 4 miles east of Talala, Okla. (Yale Univ., Peabody Mus., No. 14,469); shale near top of Wewoka formation, 5 1/2 miles west of Okmulgee, Okla.; Cherokee shale (?), Henry county, Missouri (Yale Univ., Peabody Mus., No. 14,467); Millsap Lake formation, northcentral Texas. All of these horizons are of late Des Moines age.

Genus LIMIPECTEN Girty, 1904

Limipecten Girty, 1904, U. S. Nat. Mus., Proc., vol 27, p. 721.
Deltopecten (part) of authors.

Robust, acline, symmetrical, pectiniform Aviculopectininae, especially characterized by a peculiar ornamentation; left valve with intercalate costae, crossed by the edges of regular lamellae which swing downward toward the margin between costae in short, flattened, pointed projections similar to those of Acanthopecten, somewhat more numerous and prominent on the posterior part of the shell; right valve with numerous slender intercalate costellae, which are crossed by more or less prominent fila, spaced about the same distance or closer than the costae; auricles subequal in length, ornamented with intercalate costae, lamellose projections, or both. Inner ostracum of nacreous aragonite, outer and much thinner ostracum layer composed of calcite, homogeneous in the left valve, prismatic in the right, with irregularly sized and arranged prisms. Ligament area like that of Aviculopecten; there is no shell gape; right valve nearly flat, left valve very much more convex.

Genotype—Limipeclen texanus Girty, lower Cisco. upper Pennsylvanian (Upper Carboniferous).

Range—Lower Carboniferous to Lower Permian.

This genus is closely similar to Aviculopecten, but the ornamentation is so distinctive that well-preserved and typical species of the two can be separated by even small fragments of either valve. Some unique specimens of Limipecten morsei n. sp. from the Kendrick shale in Kentucky preserve beautifully the original shell structure, with even a faint suggestion of nacreous luster. Some other specimens of Limipecten, including the type species, show the delicate lamination of the inner ostracum of nacreous structure, but some change from the original aragonite has occurred.

The only Lower Carboniferous species known to me that is probably a Limipecten is Aviculopecten docens (McCoy) (see pl. 11, figs. 6a-8b) from Great Britain. This is the species which was used to illustrate the genus Aviculopecten in McCoy's original diagnosis, and the one which has erroneously been considered as the type of Aviculopecten.

Measurements of Specimens of Three Species of Limipecten
Species Specimen Left valve Right valve
Length Height Umbonal
Auricular costae Body
Auricular costae Body
Anterior Posterior Anterior Posterior
texanus 1 a 50+ 55+ 97+   7 31       55+
2 55+ 62+ 100+ 3-4 5+ 27+ 100+ 6 7 50±
3         7       13  
4       5 6          
grandicostus 1 a 66+ 70     26±       65+
2   62   2+   23        
morsei 1 a 95 96 105±     40 100-110      
2 72± 74 95±     38 100±     52±
a. Holotype.


Plate 9, figures 2-6; Plate 10, figures 2a, c

Limipecten texanus Girty, 1901;, U. S. Nat. Mus., Proc., vol. 27, p. 722, pl. 45, figs. 1-3; pl. 47, figs. 1-3.

Shell large, orbicular, symmetrical. Left valve ornamented with high, rounded, intercalate costae that are separated by equally broad interspaces, the posterior costae not differentiated in size from the others; costae crossed by the edges of imbricate lamellae, spaced about the same as the costae; lamellae become prominent on the auricles, rising abruptly at a high angle above the general shell surface; flattened spinelike prolongations of the lamellae project from a third to a half of the distance between adjoining imbrications, and generally are obsolete on the auricles. Body of right valve nearly smooth except for fine numerous intercalate costellae, spaced lightly more distant than their breadth; they are crossed by nonprojecting obscure fila, or more properly, regular edges of lamellae more closely spaced than the costae; the edges of the lamellae become prominent and projecting on the auricles, although less than on the left valve; between every fourth or fifth costa there is a slightly broader interspace, so that there is an obscure fasciation of the costae that is most noticeable across the middle of the shell. Anterior fold of the left valve nearly straight, angular, prominent, overhanging slightly the adjoining sulcus; rear fold straight, poorly defined, in both valves; anterior auricular sulcus of left valve narrow, without costae, deep; posterior one broad, poorly defined with axis near the middle of the auricle; inner half of the sulcus characterized by faintly and more widely spread costae; cardinal costae large and prominent on both valves; crossed by projecting imbrications. Convexity of both valves in apposition 18 mm. in the holotype, a specimen 55 mm. high; outer ostracum in left valve made up of imbricating lamellae of homogeneous calcite, in the right valve composed of short polygonal prisms of variable breadth ranging up to about 35 or 40 mm. in the adult part of a shell, and having no regular arrangement in rows; the inner ostracum is delicately laminar, suggesting nacreous structure; the ligament area is underlain by a thin film of differentiated material that has a suggestion of crossed lamellar structure, but this is not certain; the ligament area of the holotype has a breadth of slightly over 2 mm.; ligament areas diverge at an angle of around 80 degrees.

Figure 26—Comparison of profiles of Limipecten texanus (upper) with Limipecten morsei (lower), showing difference in divergence of ligament areas; the left valve in both diagrams is uppermost, X 1. [Image scaled and magnifications adjusted for web presentation.]

Comparison of profiles of Limipecten texanus (upper) with Limipecten morsei (lower).

Measurements of specimens of Limipecten texanus are given in the table previous.

Comparison—This species appears to be distinguished most readily from others of the genus by the number and character of the costae, ornamentation of the auricles, and the subdued character of the concentric ornamentation on the right valve. The widely diverging cardinal areas of the two valves form a greater angle than in L. morsei.

Material—Through courtesy of the curators at the National Museum I have been able to study the type specimens of Limipecten texanus (D. S. Nat. Mus., No. 27,102), which are five in number, including the holotype. All are fragmentary but well preserved, and the valves are in apposition in several of the specimens. A single fragmentary specimen at Yale Univ., Peabody Mus. (No. 14,470) is about the same age as the types.

Occurrence—Upper Carboniferous. The types were found at Graham, Tex., associated with ironstone nodules in argillaceous, buff shale of lower Cisco age. The fact that the valves are commonly in apposition indicates that there was little or no current action during deposition of the inclosing sediments. The famous collecting horizon at. Graham is in the Wayland shale member of the Graham formation and there is little doubt but that the types of L. texanus came from this member. The single hypotype at Peabody Museum was found in the middle shale of the Jacksboro limestone 3 1/2 miles southeast of Jacksboro, Tex.


Plate 9, figures 1a, b

Limipecten texanus var. grandicostatus Girty. 1904, U. S. Nat. Mus., Proc., vol. 27, p. 23, pl. 46, figs. 1-3.

This form differs from the preceding chiefly in having broader and coarser costae on the left valve, separated by correspondingly broader interspaces. The costae on the right valve are somewhat more numerous than in L. texanus, but are otherwise quite similar. The convexity of the two valves in apposition, of a specimen 70 mm. high, is about 20 mm. In a specimen 62 mm. high, the ligament area is 5 mm. high. The angle formed by the divergence of the ligament areas of two valves in apposition is about 80 degrees.

Measurements of specimens of L. grandicostatus are given in the table previous.

Comparison—The ornamentation of the left valve in this form is similar to that of L. koninckii (Meek and Worthen) in having rather broad costae, but, as in L. texanus, spines are obscure or lacking on the auricles. The right valves of L. koninckii and L. grandicostatus differ in the possession of prominent fila in the former species.

Material—This description is based on two of the four types (U. S. Nat. Mus., No. 27,103), two specimens being too badly weathered to be of much aid. The two valves are in apposition, and the material is well preserved, retaining the entire ostracum. The shell substance is stained a limonite brown throughout.

Occurrence—Upper Carboniferous. Argillaceous buff shale, associated with ironstone concretions. Wayland shale, Graham formation, lower Cisco, at Graham, Tex.


Plate 10, figure 1

Aviculopecten koninckii Meek and Worthen, 1860, Philadelphia Acad. Nat. Sci., Proc., p. 453; 1866, Illinois Geol. Survey, vol. 2, p. 328, pl. 26, fig. 8.

Shell large, orbicular, longer than high; right valve slightly flatter than the left, ornamented with at least 80 slender, closely spaced intercalate costellae crossed by fine raised fila, about 10 of which occupy a distance of 4 mm. on the anterior slope of the mid part of the shell; besides a moderately prominent cardinal costa, there are six costae on the posterior auricle; umbonal angle in the holotype (right valve) 109 degrees; height,78 mm.; length, 87 mm.; convexity, 8 mm.; hinge length, about 77 mm.; the posterior sulcus, like that of L. texanus, is broad, illdefined and nearly or quite noncostate over the inner half of the sulcus; axis of the sulcus nearly bisects the posterior auricle which is set off by narrow obscure, nearly straight umbonal fold; anterior fold essentially straight; outer ostracum prismatic, inner ostraeum macreous; costae of the left valve are coarser than those of the right, spaced 14 to 20 mm. apart near the ventral margin where the shell was 80 mm. high.

The species is known from only one specimen, a right valve, to which is clinging a small fragment of the complementary valve. It is always difficult to recognize a pectinid species from the right valve, because the right valves in similar species of a genus .are likely to look alike. It seems, however, that this form is sufficiently distinct from other limipectens to permit recognition.

Comparison—This form is distinguished by the wide umbonal angle, large number of costellae on the right valve, and by its elongate form.

Material—The holotype, a right valve, (Univ. Ill., No. 12,877) was made accessible to me through the generosity of Dr. J. Marvin Weller. The specimen is well preserved, showing the complete ostracum of the shell, with the characteristic structure of Limipecten.

Occurrence—Upper Carboniferous, in black, pyritiferous, fine-grained limestone, apparently of the concretionary kind sometimes found in black fissile shales, Des Moines subseries, Pennsylvanian, Alpine, Iowa. According to Doctor Marvin Weller (personal communication) this horizon may be about the same as the Illinois Coal No. 1.


Plate 1, figures 8, 16; Plate 10, figures 5-7b

Deltopecten texanus Morse, 1931, Kentucky Geol. Survey, vol. 36, p. 317, pl. 51, fig. 1.

Shell large, orbicular, about as long as high; left valve with rather broad, irregular intercalate costae, of which there are about 40, spaced approximately as far apart as the breadth of the coarsest costae; costae crossed by the edges of somewhat irregular imbricating lamellae, spaced about the same distance as the ribs; the intercostal projections commonly reach less than half of the distance between adjoining edges of the lamellae, becoming progressively more prominent from front to rear en the shell surface; anterior auricle abruptly set off by an acute, slightly overhanging fold which curves outward almost imperceptibly; there is no posterior fold; right valve ornamented in the adult with 55 or more slender, closely spaced, intercalate costellae crossed by prominent rather irregularly spaced fine fila, spaced about the same as the costellae across the middle of the valve, but becoming crowded over the marginal areas of the shell; anterior umbonal fold nearly straight, angular; posterior one obscure, straight; ligament area as in L. texanus, except that the area of left valves makes a small angle with the plane of the valves, instead of being nearly parallel to it; in L. morsei the plane of the valves nearly bisects the angle between the diverging ligament area of the two valves; valves of subequal convexity, the right being only very slightly less convex than the left. There are at least three costellae on each rear auricle of the holotype; costae lacking near the inner part of the angular auricular sulcus, this area being covered only by fine imbrications; the projecting short spines on the inner part of the very broad posterior sulcus of the left valve become somewhat more sparse across the auricle toward the hinge margin.

The preservation in the type specimens of L. morsei is exceptionally good. The inner ostracum shows a faint iridescence suggestive of the original mother-of-pearl luster, and exhibits in thin sections the exceedingly delicate lamination of nacre. By means of Meigen's method for identification of aragonite, the inner ostracum was found to be unaltered aragonite. The outer ostracum is perfectly preserved in both valves, consisting in the left valve of thin imbricating lamellae of homogeneous calcite, and in the right valve of short polygonal prisms having a maximum diameter of about 30 microns. The hypostracum layer is well-preserved aragonite. It is fibrous rather than prismatic, and cross sections of the fibers are much too irregular to be called polygonal. The convexity of a specimen 74 mm. high with both valves in apposition is 25 mm. The hinge length of a specimen 96 mm. high is 80 mm.

Measurements of specimens of L. morsei are given in the table previous.

Comparison—This species differs from L. koninckii in being less elongate, markedly higher, and in having a smaller number of costae on the right valve. It is distinguished from L. texanus and L. grandicostatus by having a greater development of the short spines on the posterior part of the left valve, and in having prominent fila on the right valve, rather than only the obscure flattened edges of lamellae. Furthermore, the right valve in L. morsei, as well as in L. koninckii, is somewhat more convex than in L. texanus and grandicostatus, so that the ligament area in the two valves of the present species are about equally disposed in relation to the plane of the valves. In the two latter species, from the Graham shale, on the other hand, the ligament area in the left valve is more nearly parallel to the plane of the valves. The body costae of the left valve are more numerous in the present species than in the Texas forms. The name is given in honor of Prof. William C. Morse.

Figure 27—Profile of Limipecten morsei, X 1. [Image scaled and magnifications adjusted for web presentation.]

Profile of Limipecten morsei.

Material—I am indebted to Professor Morse for the loan of the remarkable specimen from Kentucky, selected as the holotype. The specimen is now at Mississippi State College. Two other specimens, topoparatypes (Yale Univ., Peabody Mus., No. 8,146) were used in formulating the description. This material is the finest that I have seen of Paleozoic Pectinacea in the remarkable preservation of the original aragonite of the inner ostracum.

Occurrence—Upper Carboniferous. The two topoparatypes are labeled Kendrick shale, Cow Creek, Floyd county, Kentucky. The holotype was found at the same horizon at the Kendrick homestead at the head of Cow Creek. This horizon is high in the Pottsville, Des Moines subseries, Pennsylvanian.


Plate 10, figures 3, 4

Deltopecten occidentalis var. latiformis Shimer. 1926, Canada Geol. Survey, Bull. 42, p. 76, pl. 7, figs. 11a, b, 12.

Shimer's description:

Shell flabelliform, with transverse diameter (from anterior to posterior border) slightly greater than the distance from the hinge-line to the basal border; in consequence, the angle formed at the beak between the anterior and the posterior umbonal slopes is broad. slightly exceeding a right angle. Hinge-line nearly or quite equalling the greatest length of the valves. Length. the diameter from the anterior to the posterior margin, 30 mm.; height from hingeline to basal margin, 23 mm.; greatest thickness of the conjoined valves 8 mm. Angle to divergence of the umbonal slopes at the beaks 100 degrees (in one specimen 90 degrees).
Left valve sloping broadly and flatly in all directions from the slightly convex umbonal region. Ears nearly equal in size, the anterior the more obtuse and defined by a deeper sinus from the body of the shell; it is marked by six or seven radiating ribs which are finely crenulated by concentric striae. Posterior ear separated from the body of the valve by a broad and shallow depression; on this ear the concentric markings are the more conspicuous and the radiating striae are fine and numerous—18 or 20 in number. Surface of valve marked by strong radiating costae between which are Irorn one to three intercalated weaker striae; only the stronger costae are present at the beak, whereas at the ventral margin there are. in a space of 6 mrn., about ten striae, of which four are strong.
Right valve nearly flat and much more faintly ribbed than the left, with finer striae of nearly equal size. Sinus separating the anterior ear from the body of the shell much sharper and deeper than on the left valve.

Through the courtesy of Dr. E. M. Kindle of the Canada Geological Survey, I have had an opportunity to study the paratypes and a squeeze of the holotype of this species. The material is preserved as impressions in a hard, white, quartzose sandstone or quartzite. The details of ornamentation are very poorly preserved. I have not seen the left valve, said to be preserved in the holotype, and the best paratypes are right valves, so I cannot add anything to Shimer's description. It is not possible to make an accurate count of costae in the material at hand, but it appears that there are about 65 or 70 costae on the shell body of the right valve. The costae are slender and crowded; they appear to be intercalate, although this is not certain. A poorly preserved fragment of a left valve, originally having a height of at least 32 mm., shows at least 10 evenly spaced intercalate costae. They are crossed by fine regular fila. The anterior auricle of the right valve in one specimen has 5 or 6 costae, including the cardinal costa. The right valve is by no means flat, but it appears to be less convex than the left. The umbonal folds are nearly straight in right. valves, diverging at 90 to 100 degrees.

Comparison—The general aspect of the species suggests Limipecten, but assignment to this genus is by no means certain, considering the imperfections of the types. In no known Aviculopecten, however, are the costae of the right valve so numerous. In the more typical species of Aviculopecten, the umbonal slopes flare outward in a decided curve, whereas in the present forms they are nearly straight. The only Limipecten that has approximately the shape of the L. latiformis is L. koninckii (Meeks and Worthen), of Des Moines age. It is hardly possible to confuse these forms, in view of their great difference in age.

Material—The type collection (Victoria Memorial Mus., No. 4,863, Ottawa) includes several specimens, six of which I have seen, all poorly preserved, as molds and casts in coarse quartzite.

Occurrence—Permian of the Lake Minnewanka region, Alberta, (Shimer's loc. 14, section 1).


Plate 11, figures 5a, b

Shell large, about 50 mm. long and high; orbicular; acline and symmetrical; umbonal folds hardly distinguishable, curving outward equally; sulci broad and ill-defined, coinciding in breadth to the entire area of either auricle; shell body ornamented in the holotype with 62 slender crowded costae in four ranks, spaced slightly closer than their breadth; costae crossed by a rather striking concentric ornamentation; up to a shell height of 8 mm. the costae are smooth, from thence to a height of about 17 mm. the ornamentation, although finer, becoming like that of typical Limipecten, having acute downward projections of the fila, or imbricating lamellae, between costae, and finally toward maturity the lamellae becoming vaulted into short prominences on the costae while the pointed projections between the costae become less conspicuous; ornamentation of the two auricles similar and clearly set off from that of the shell body by abrupt. widening of the interspaces between costae, and decrease in size of the costae to faint costellae; on the anterior auricle there are about 10 costellae which are crossed by the edges of irregular imbricating lamellae, giving rise to short vaulted projections on the costellae; dorsal margin of each valve occupied by a relatively enormous cardinal costa having transverse, scale-like projections where it is crossed by the imbricating lamellae; umbonal angle in the holotype about 105 degrees.

Comparison—This curious form does not need to be compared with any other American species. It certainly is not a typical Limipecten, as is especially indicated by the obsolescent character of the anterior umbonal fold. A deep anterior sulcus and overhanging angular fold is characteristic of most limipectens. The ornamentation, however, is similar to that of Limipecten, and there is now no more appropriate genus in which to place it.

Material—Only one specimen of L. wewokanus, a well-preserved left valve, is known. I consider it a poor practice to describe a new species from only one specimen, but the present form seems so distinctive that there should be no difficulty in recognizing it. The holotype is Kansas Univ. Paleont. Type Coll., No. 374.

Occurrence—Upper Carboniferous, very thin ferruginous, highly fossiliferous lens of limestone in gray argillaceous shale. Wewoka formation, near top of middle shale, quarry at spillway, east end of Lake Okmulgee, 5 1/2 miles west of Okmulgee, Okla. Des Moines subseries.

Genus ACANTHOPECTEN Girty, 1903

Acanthopecten, GIRTY, 1903, U. S. Geol. Survey, Prof. Paper 16, p. 417.

Orbicular, acline or slightly prosocline Aviculopectininae, about as long as high, with moderately long, slender auricles, the posterior only slightly longer than the anterior; simplicicostate, i. e., without increase in number of costae after a very early stage; left valve with from about 15 to 50, rarely more than 25, broad closely spaced costae, separated by angular shallow grooves; along the crest of each costa there is a more or less distinct narrow, rounded ridge or keel, very obscure in some forms, which may be considered as the primitive costa (because, as traced toward the beak, the angular grooves of the interspaces disappear, leaving only the narrow costellae, which if continued to their origin, are seen in some instances to be intercalated between others, as in Aviculopecten); at a juvenile stage the costae are crossed at right angles by regular raised fila, which later become extended downward between costae in sharp proj ections; with increasing maturity, particularly coarse fila are introduced on auricles and shell body at regular wide intervals, and these ridges extend downward between costae in short, stout spines having a U-shaped cross section, with the convex surface inward; right valve nearly flat, almost smooth, except for widely spaced slender costellae that correspond in number and position to the interspaces of the opposite valve; structure of inner ostracum unknown, outer film of ostracum apparently homogeneous or granular in the left, and definitely prismatic in the right valve, with the prisms somewhat more regular in form and size than is commonly the case in the subfamily, ranging in diameter up to 25 microns; hinge as in Aviculopecten; musculature unknown; posterior umbonal folds outcurved, poorly developed, nearly obsolete in right valve; anterior folds curved outward, sharply angular, that of the left valve overhanging an equally narrow and angular anterior sulcus; sulcus of rear auricle in each valve broad, shallow, corresponding in breadth with the auricle; auricular costae few, widely spaced; cardinal costae particularly coarse, rugose where crossed by fila, particularly on the anterior auricle.

GenotypePecten carboniferus Stevens, from the Centralia formation, Missouri subseries, Illinois.

Range—Mississippian to Permian.

Remarks—This genus has been widely misunderstood because of the rarity of specimens retaining the inner ostracum and hinge. Meek, with his usual keen perception, suspected the true relationships when he wrote of Acanthopecten carboniferus:

The only specimens of this species I have seen consist entirely of what seems to be the thin outer layer of the shell, in which there appears to be a prismatic structure, as seen by the aid of a microscope and a strong transmitted light. They show no flattened cardinal plate, but a furrow along the inner side of the hinge margin of each valve. The cardinal plate or area was doubtless composed, as in other cases, of the inner laminated portion of the shell, that has been destroyed during the fossilizing process; if not, it would seem to be a new genus. (Meek, 1872, p. 194.)

I have been able to recognize the oblique resilifer and ligament area of the Aviculopectininae in specimens from the Westerville oolite at Kansas City, and in certain other specimens. Every specimen that I have seen preserved in shale has lost the inner ostracum, with the characters of musculature and hinge, while only a thin outer film of calcite remains. On the other hand, the inner ostracum of shells preserved in limestone is, in most instances, so badly recrystallized that the rock matrix cannot be readily separated from the inner part of the shell.

The difficulties in the discrimination of species in this genus are manifold. In the first place, the range of specific variation in the genus seems to be small, i. e., all of the several described species of Acanthopecten, the world over, are surprisingly alike in general features, so that the species must be differentiated on more or less obscure characters. Secondly, collections containing as many as two or three well-preserved specimens from one locality are rare. There are only two lots at my disposal in which there are enough specimens to attempt a statistical study. One of these occurs in a fine clay matrix, the other in oolitic limestone, and the preservation of the ornamentation is so different in the two that they can scarcely be compared. Specimens from limestone are almost always misleading because the spines and vaulted frills are generally broken away with the matrix. On the other hand, shale specimens are commonly distorted through compression.


Plate 12, figures 8a-10

Pecten carboniferus Stevens, 1858, Am. Jour. Sci., (2), vol. 25, p. 261.
Pecten hawni Geinitz, 1866, Garb. und Dyas in Neb., p. 36, taf. 2, figs. 19a, b.

The original types of this species appear to have been lost, but there are very good grounds for its continued recognition. Two topotypes were lent to me by Dr. J. Marvin Weller, and one of these specimens, a left valve, is the basis for the following description.

Shell acline, orbicular, with 16 broad flattened costae, separated by narrow, angular furrows which become less angular with growth; crest of each costa surmounted by a high and narrow costella which becomes hemicylindrical near the ventral margin; slopes of the costae on either side of the median costellae, or keels, are slightly convex; surface covered with two sets of fila—coarse, widely spaced first order ones separated by many fine second order ones; at a very early stage the second order fila probably extended directly across the costae, but throughout the preserved part of the shell at hand, the fila are curved downward between costae into short pointed projections. Up to a height of about 7 mm., two or three of the small fila are fascicled over the costae to form a single coarser one; these modified fascicles are separated by three to four normal; the first coarse filum originates at a shell height of 6 or 7 mm. and thereafter the large fila periodically appear at progressively increasing intervals; they project ventrally into stout spines between the costae, extending about one third to one half of the interval between successive coarse fila; spines U -shaped in cross section, with concave surface directed outward; large fila in the specimen at hand are not vaulted into projections over the costae; posterior auricle has a large, oddly angular cardinal costa, which is apparently nearly quadrate in cross section; there are five obscure costellae on this auricle and the inner one is recognized only with difficulty. Where the large fila cross the auricular costellae, a large channeled spine is developed like those on the shell body, but it was not possible to illustrate them in the figured squeeze; anterior auricle and umbonal fold lacking in the specimen at hand; internal mold exhibits a narrow but distinct, smooth, flat ligament area and the poorly exposed impression of a resilifer; intervals between the last five coarse fila, measured across the middle of the shell: 1.5 mm., 2.6 mm., 3.0 mm., 3.5 mm.

Of 15 left valves from the Willard shale at Rockford, near Nebraska City, Neb. (U. S. Nat. Mus., No. 6,508), 6 have 17 body costae, 7 have 16 body costae, and there is one each with 15 and 18 costae. In this lot the number of anterior costae ranges from one to three, and the posterior ones from two to three. In five right valves from this suite there are three with 15 costellae and one with 17; in every one there are three anterior costae and no posterior ones.

The following measurements were obtained in the topotype, a left valve, from the Centralia formation, in Illinois: length, 19 mm., height, 17 mm; umbonal angle, 98 degrees.

The topotype specimen at hand is preserved in shale, and has been flattened slightly. Apparently the original convexity was about 3 or 4 mm. Other specimens retaining the anterior part of the shell have a slender anterior auricle, a deep angular sulcus, crossed by projecting imbricating lamellae, and a narrow overhanging anterior umbonal fold.

It is very probable that more than one species is included here under A. carboniferus. Most of my specimens occur in shale and the preservation generally is poor. When it is possible to compare directly a representative collection from the horizon of the topotypes with large collections from other horizons undoubtedly a further discrimination of species will be found desirable.

The types of Geinitz's Pecten hawni came from about the horizon of the Willard shale at Nebraska City. If it is possible to separate A. carboniferus from the Nebraska City material, when better collections of typical oarboniferus are secured, the name Acanthopecten hawni (Geinitz) will have to be applied to the Nebraska City form.

Both of the species Pecten broadheadi Swallow (St. Louis Acad. Sci., Trans., vol. 2, p. 97) and Pecten armigerus Conrad (Pennsylvania Geol. Soc., Trans., vol. 1, pt. 2, p. 268, pl. 12, fig. 3) are acanthopectens, but they are too poorly described for recognition, except through the unwarranted assumption that there is only one species of the genus in our Pennsylvanian rocks. The types of these species are lost or destroyed and their original localities and horizons are unknown.

Comparison—This species, on the basis of several rather poor specimens, chiefly from the Missouri and Virgil subseries of Kansas and adjacent states, appears to be distinguished by low convexity, rather large number of coarse fila, particularly narrow and distinct keels or costellae on the crests of the costae; also, there seems to be no tendency for the coarse fila to form vaulted projections over the costae. The topotype described above is nearly as large as any specimen of the species in the collections at hand.

Material—Two topotypes were available to me, but only one is sufficiently well preserved to be of value. It is a left valve preserved. in shale, retaining an exceptionally fine external mold and a rather poor internal mold upon which some of the external ornamentation appears to have been impressed. The specimens belong to the Illinois Geological Survey.

Occurrence—Upper Carboniferous. This species, as here classified, occurs through much of the Pennsylvanian section, from beds of Des Moines to Wabaunsee age, through the Mid-Continent region. The type specimens are from the Centralia formation, Missouri subseries, Crooked Creek, near Centralia, Marion county, Illinois. Other specimens in the Mid-Continent region have been found in Des Moines beds (Altamont limestone), Missouri beds (Raytown limestone, Jacksboro limestone, Francis formation), and in Virgil beds (Kereford limestone, Ervine Creek limestone, White Cloud shale, Haskell limestone, Howard limestone, Maple Hill limestone, Willard shale, Graham formation).


Plate 12, figures 1a-5

Acanthopecten carboniferus Sayre, 1930, Kansas Geol. Survey. Bull. 17, p. 121, pl. 12, figs. 5, 6.

Left valve acline, symetrical, markedly convex, nearly hemispherical in full-sized specimens; costae broad, rounded, commonly with only an obscure keel on the younger stages; small fila absent except on the very young parts of the shell at the umbo; coarse fila (more properly, the edges of imbricating lamellae) numerous, the first one appearing generally at a shell height of 4 to 6 mm., extended generally into strongly protruding vaulted projections over the costae, most prominent over the anterior part of the shell body; anterior fold narrow, sharply angular, projecting distinctly out over the deep and angular noncostate auricular sulcus; posterior fold small, angular, and distinct; posterior sulcus broad, right valve unknown; in the holotype the concentric lamellae are added respectively at the following shell heights; 4, 6, 7, 8, 9, 11, 13.5 16.5, 20, 24, 28, and 31.5 mm.

Moderate variation occurs in the prominence of the vaulted lamellae on the costae, and in the prominence and breadth of the more or less obscure ridge or keel on the costae. Far more confusing is the condition of preservation, because the details of surface ornamentation generally are broken away when the specimens are removed from limestone matrix. If allowances are made for preservation, there is little difficulty in recognizing this species.

Comparison—This species is readily distinguished from A. carboniferus (Stevens) by its great convexity, rounded costae, with broad, generally obscure costellae along their summits, and the projecting rounded and vaulted imbrications over the costae. The coarse fila are projected in such a way that they are more accurately described in A. meeki as the edges of imbricating lamellae, whereas in A. carboniferus they are vertically elevated ridges or fila.

Material—The species is based on a large number of left valves from the Westerville oolite of the Kansas City region, and one particularly fine specimen from an unknown locality in Douglas county, Kans. Holotype and three topoparatypes, Yale Univ., Peabody Mus., No. 8,148; five topoparatypes, Yale Univ., Peabody Mus., Nos. 14,471, 14,472; 25 topoparatypcs, Kansas Univ., Paleont. Type Coll., No. 375; paratype, Kansas Univ., Paleont. Type Coll., No. 376.

Occurrence—Upper Carboniferous. The species appears especially to characterize the limestones of the middle and upper part of the Missouri subseries. Many individuals, including nearly all of the types, were found in the Westerville oolite, at various places around Kansas City. One fine paratype, the best specimen in the collection, came from an unknown locality in Douglas county. The matrix of this specimen is identical with a peculiar kind of limestone which occurs at the top of the Captain Creek limestone (Lansing) in Douglas county. On the other hand, the horizons represented in the county range from upper Lansing to lower Shawnee, and this specimen might have come from anyone of several limestone formations. Other specimens were found in the Argentine limestone, Kansas City; Drum oolite, 1 mile east of Independence, Kan.; Captain Creek limestone near Eudora, Kan., and north edge sec. 10, T. 13 S., R. 21 E., Kansas; Merriam limestone, south line sec. 17, T. 17 S., R. 22 E., Kansas; Iatan limestone, 2 miles northwest of Nehawka, Neb.; Iola limestone, Iola, Kan.; Farley limestone, south of DeSoto, Kan.; Olathe limestone, Fredonia, Kan.

Measurements of Left Valves of Acanthopecten meeki Newell, n. sp.
Auricular costae Body
Anterior Posterior
1 a 34 32   8 98     18 10
2 16 16 12± 2.5 95 2   18 7
3 19 20   3.5 96   5 16 7
4 16 16 13± 3+ 90± 2 5 15 6
5 21.5 20 13 4.5 100 3   18 11
6 19 18.5   4.5 85   4 18 8
7 26.5 24   6 103     18 10
a. Holotype.


Plate 12, figures 7a, b, 18-15b

Pecten (Monotis?) Coloradoensis Newberry, 1861, Ives Colo. Expl. Exped., p. 129, pl. 1, figs. 6, 6a.

Shell characterized by a relatively large number of costae, 23 in a nearly complete hypotype; a large number of closely spaced coarse, raised fila that extend across shell body and auricles, extended into spines between the costae, as long or longer on the mature part of the shell than the distance between successive fila. Posterior umbonal fold low, obscure, bounded on the inside by an almost indistinguishable flattening or sulcus; anterior one angular; but low and not overhanging the sulcus; auricular sulci broad, rounded; posterior auricle poorly defined, possessing one or two obscure costellae; anterior one without costellae. Only one order of fila is observed; at a shell height of 6 mm. the fila are slightly finer and more widely spaced than the costae, extending straight across costae and interspaces; subsequent fila become extended ventrally into sharp points between costae and take on progressively the appearance of the thickened edges of imbricating lamellae, but they generally are not projected outward from the main surface as vaulted protuberances; the fila continue to be much finer than the costae and their spacing progressively increases at a lower rate than the divergence of adjoining costae, so that at a mature stage the costae are wider apart at their crests than one or two successive fila; between a shell height of (3 mm. and 27 mm. 16 of these spinose fila are added, the last two being spaced about 2 mm. apart; shell of moderate convexity, nearly even in all directions. Dimensions for a well preserved external mold of a left valve; height, 27 mm.; length, 25 mm.; hinge length, about 23 mm.; convexity, about 6 mm.; number of body costae, 23. The umbonal angle cannot be measured satisfactorily because of the poorly defined posterior fold, but it may be estimated at about 1W degrees. The species attains a large size, one topotype measuring 50 mm. in height.

Comparison—This species is so distinctive that it scarcely needs comparison with Pennsylvanian forms. The large number of costae, closely spaced and numerous concentric ridges, and poorly defined rear umbonal fold are the most obvious characters by which the species may be recognized.

Material—The two figured syntypes (Columbia Univ., Nos. 6,392G and 14,203), generously lent to me by Dr. Marshall Kay, are fragments of left valves preserved in drab dolomitic limestone in which are the altered remains of many fenestrate and fistuliporid bryozoans. The better preserved, though more fragmentary specimen (14,203) is here designated as the lectotype. Two other specimens from the same horizon and region as the types are preserved in chert concretions, one as a nearly complete external mold (Yale Univ., Peabody Mus., Nos. 14,473, 14,474). Six fragmentary hypotypes, occurring in drab, soft dolomitic limestone of the Word formation, belong to the Texas Bureau of Economic Geology.

Occurrence—Permian. The types of A. coloradoensis are labeled "Upper Carboniferous, north of Little Colorado River, New Mexico," this area now being included in Arizona. The dolomitic limestone is the Kaibab. Two of our hypotypes came from the Kaibab limestone at Bass Ranch, Grand Canyon, Ariz., and at Arden, Las Vegas quadrangle, Nev. Other specimens are from the Word formation, Glass Mountains, western Texas. Both the Kaibab and Word formations are well up in the Permian.

Measurements of Left Valves OF Acanthopecten coloradoensis (Newberry)
Horizon Specimen
Auricular costae Body
Anterior Posterior
Kaibab 1   51   10        
Kaibab 2 25 27 23± 6 115±   2 23
Word 3 26 27 24 6 115±     21


Plate 12, figure 12

Aviculopecten delawarensis Girty, 1908, U. S. Geol. Survey, Prof. Paper 58, p. 437, pl. 23, figs. 2, 2a.

Through the kindness of Doctor Girty I have had opportunity to study the type specimen of A. delawarensis. It appears to be a typical Acanthopecten, as evidenced by its symmetry, form, grooved interspaces, keeled costae, and constant number of costae during ontogeny. The characteristic spines of this genus are not visible, but the holotype is so poorly preserved that the ornamentation is not distinct. Although the species was originally described as being oblique it appears to me that the present outline of the specimen is misleading as the result of being slightly broken away at the rear margin. There are 18 or 19 costae on the shell body. Probably this species cannot be recognized widely until topotype specimens are secured and detailed study made.

ComparisonAcanthopecten delawarensis is comparable in general to A. coloradoensis, but appears to have fewer costae, the latter having 21 to 23 costae (probably, also, more and less), whereas the single specimen of A. delawarensis has only 18 or 19.

Material—A single specimen, the holotype, U. S. Geol. Survey, Type Coll., No. 417, furnished the basis for my observations.

Occurrence—Middle Permian, drab dolomitic limestone of the Delaware Mountain formation, Guadalupe Mountains, western Texas.


Plate 12, figure 11

Aviculopecten laqueatus Girty. 1908, U. S. Geol. Survey, Prof. Paper 58, p. 439, pl. 9, fig. 11.

Shell of moderate size, suborbicular, slightly extended anteriorly to produce a very slight opisthocline obliquity; auricular costae absent, shell body with 21 broad, flattened costae, each surmounted by a narrow, distinct keel or costella; interspaces narrow, trough-shaped or grooved, distance between keels about four times their breadth; eight or more concentric, coarse fila extend directly across interspaces and costae without deflection, producing a striking panelled ornamentation, each rectangle being about twice as high as broad; spinose ornamentation characteristic of most acanthopectens absent. Measurements of holotype: length, 20 mm.; height, 21 mm.; hinge line, 16 mm.; convexity, 5 mm.; umbonal angle, 110 degrees; body costae, 21.

Comparison—No other American species resembles this one. The absence of the intercostal spines which are characteristic of Acanthopecten, taken with the proportions of the shell, distinguish this form. However, the peculiar keeled costae are found only in Acanthopecten and the orbicular shape and symmetry of A. laqueatus identify the species with Acanthopecten.

Material—The holotype, U. S. Geol. Survey, Type Coll., No. 416, served as the basis for my observations.

Occurrence—Upper Permian, drab dolomite of the Capitan limestone, Guadalupe Mountains. western Texas.

Genus ANNULICONCHA Newell, n. gen.

Orbicular, acline or slightly prosocline Aviculopectininae, ornamented on auricles and shell body by two ranks of distinct fila; at a mature stage a few irregular, ill-defined radial ridges appear, but they do not occur on young individuals; auricles of nearly equal size and shape, with acute terminations; anterior umbonal fold of left valve narrow, subangular, posterior one lacking; anterior sulcus deep, narrow, with a steep or perpendicular inner boundary; posterior sulcus, broad, shallow; cardinal costae absent; right valve apparently similar to the left in ornamentation, but slightly less convex; shell structure and musculature unknown.

GenotypeAviculopecten interlineatus Meek and Worthen, LaSalle limestone, Missouri subseries, LaSalle, Ill.

Range—Mississippian (Lower Carboniferous) to Permian.

This genus is similar in form to species of Acanthopecten and Girtypecten, and the very early growth stages of the three genera are similar in form and ornamentation. It seems rather probable that these three genera are more closely related to each other than to other Aviculopectininae.

Owing to the extreme rarity of specimens of Annuliconcha, no satisfactory basis has yet been discovered for recognition of more than one species in the American Pennsylvanian rocks. Ordinarily, too, the specimens are found in hard limestone and much of the projecting ornamentation is lost when the matrix is broken away, so that limestone specimens commonly give an erroneous idea of the ornamentation.

Undoubted representatives of the genus occur in the Word formation (Permian) of the Glass Mountains, but these specimens are too poorly preserved to warrant specific identification.


Plate 13, figures 6a-10

Aviculopecten interlineatus Meek and Worthen, 1860. Philadelphia Acad. Nat. Sci., Proc., p. 454; 1866, Ill. Geol. Survey, vol. 2, p. 329, pl. 26, figs. 7a, b.
Posidonomua lasallensis Miller and Gurley, 1896, Illinois State Mus. Nat. History, Bull. 11, p. 12, pl. 1, figs. 17, 18.

Shell, exclusive of auricles, circular; there are two ranks of fila, very coarse ones separated by several fine ones, the coarse fila becoming progressively small on the umbonal area, where they appear at a shell height no greater than 0.5 mm., the fine fila being first visible between the coarse ones at about 1 mm. In a well-preserved topotype 14 mm. high, there are 15 of the large fila, and there are at least two more in the holotype having a height of 18 mm.; the tenth coarse filum is introduced at a shell height of 4 mm., the eleventh at 5 mm., twelfth at 6.5 mm., thirteenth at 8 mm., fourteenth at 10.5 mm., fifteenth at 14 mm. Between the twelfth and thirteenth fila there are 9 or 10 of the small closely spaced ones; in the following interspaces between the coarse fila there are respectively 10, 14, 14, and 16 of the small ones.

The large fila have rounded summits and parallel, perpendicular sides. At a height of 8 mm., in one specimen, and 10 mm. in another, about 24 radial low, rounded ridges appear and extend outward toward the shell margin, but they do not occur on the auricles. At each large filum they are interrupted without modifying the filum, and commonly they are offset slightly at successive fila. At a mature stage the outer surface of the coarse fila is obscurely crenulated, without, however, any necessary correspondence to the radial ridges. One specimen, showing part of the inner margin, has a series of papillae along the inner surface of the margin. In a shell 14 mm. high, the papillae are spaced a little less than 1 mm. apart along the ventral margin. Beyond a height of 13 or 14 mm., each successive interspace between the large fila is depressed distinctly below the level of the previous one, like the steps of stairs. The shell gapes distinctly at both ends.

Measurements of Left Valves of Annuliconcha interlineata (Meek and Worthen)
Specimen No. Height,
1 a 18 20 16 100
2 14     103
a. Holotype

Through the courtesy of Drs. Carey Croneis and J. Marvin Weller, I have had opportunity to examine and directly compare the holotypes of Aviculopecten interlineatus Meek and Worthen and Posidonomya lasallensis Miller and Gurley. The latter proves to be a distorted juvenile of the former. The two come from the same locality and horizon.

Figure 28—Juvenile growth stages of Annuliconcha interlineata (camera lucida drawing, X 25). [Image scaled and magnifications adjusted for web presentation.]

Juvenile growth stages of Annuliconcha interlineata.

Comparison—This is the only species of Annuliconcha that I have been able to recognize in the material at hand. However, each one of our few specimens is poorly preserved, and I was forced to depend chiefly on two borrowed specimens to describe the species.

Material—A fine topotype figure was lent me by the curators of the National Museum (No. 80,348). The holotype is Univ. Illinois, No. 10,922, and the holotype of Posidonomya lasallensis, Univ. Chicago, No. 6,612.

Occurrence—Upper Carboniferous. The type came from the Lasalle limestone, Missouri subseries, Lasalle, Ill. Other specimens were found in the Des Moines subseries (Cherokee shale, sec. 1, T. 31 S., R. 23 E., Cherokee county, Kansas; Oologah limestone, Garnett quarry, northeast of Tulsa, Okla.); in the Missouri sub series (Argentine limestone at Kansas City; Stoner limestone, Farley, Mo.; Dewey limestone, Dewey, Okla.; Adams Branch limestone, quarry, 3 miles northwest of Bridgeport, Tex.); and in the Virgil subseries (Willard shale, one half mile north of the mouth of Weeping Water Creek, Nebraska.) All belong to the Pennsylvanian series, Upper Carboniferous.

Genus GIRTYPECTEN Newell, n. gen.

Prosocline or acline, suborbicular Aviculopectininae, ornamented on the left valve with coarse, widely spaced costae which are intersected by almost equally and similarly spaced concentric ridges that continue across the subequal acute auricles; long, cylindrical, erect spines rise from the intersections of the coarse radial and concentric ornamentation; interspaces between the coarse costae, and surface of the auricles ornamented with fine, widely spaced, intercalate costellae; there is a distinct cardinal costa on the left valve; auricular sulci well defined, and umbonal folds prominent, corresponding to marginal, first order costae of the shell body, the posterior fold being distinctly longer than the anterior one; byssal sinus obsolescent; ligament area aviculopectinid with the greater part of the resilifer lying behind the beaks; early juvenile stages like corresponding stages of Acanthopecten and Annuliconcha in having an elongate subquadrate shape and an ornamentation of regular fila; right valve unknown; shell structure unknown.

GenotypeAviculopecten sublaqueatus Girty, from the Permian of western Texas.

Remarks—The genus is represented in the Permian of Sicily by Pseudomonotis fimbriata Gemmellaro. The genus is not yet recognized in Pennsylvanian rocks. Pterinopecten tesselatus (Phillips), as figured by Hind, from Lower Carboniferous beds of Great Britain, and Aviculopecten tesselatus (Phillips) from the Lower Carboniferous of New South Wales, Australia, bear a resemblance to Girtypecten, but I am not convinced that they belong to this genus.

Measurements of Left Valves of Girtypecten sublaqueatus (Girty)
Height /
length /
Convexity /
No. auricular
Anterior Posterior First
1 17 17 1.00 17 1.00 2.5 0.14 84 3 5 7 13
2   30       4.5 0.15 78     8 15
3 44 40± 0.91 35 0.79 5.5 0.14 93     7 30+


Plate 13, figures 11-14b

Aviculopecten sublaqueatus Girty, 1908, U. S. Geol. Survey, Prof. Paper 58, p. 440, pl. 9, fig. 12 (actual date Feb., 1909).

Acline, or slightly prosocline shells with nearly equal, extended auricles; the anterior auricular sulcus sharply incised, bounded within by a nearly perpendicular slope of the adjoining umbonalf'old that corresponds to the anterior first order costa of the shell body; posterior sulcus broad, its axis nearly bisecting the auricle, bounded within by a well defined, narrow umbonal fold which coincides with the posterior first order costa of the shell body; shell body ornamented by six to eight coarse, widely spaced costae which are intersected by almost equally coarse concentric ridges or fila which extend across the auricles as well as shell body; spaced a little more widely than the costae; auricles and spaces between first order costae ornamented by widely spaced, fine, subequal intercalate costellae, distributed in as many as five ranks in full-sized shells; in a shell 40 mm. high there are five small costellae near the margin between the large first order ones; in a shell 7 mm. high there are only three supplementary costellae in the interspaces between first order costae; the first order costae appear simultaneously 0.5 mm. from the end of the beak, the second order costellae appearing somewhat irregularly between 5 and 7 mm. from the beak; there are four of the coarse fila at a shell height of 0.5 mm. where the costae originate, at 17 mm. there is a total of 17 fila, and at 40 mm. about 25 fila; long heavy, cylindrical spines rise almost perpendicularly from the points of intersection of fila and first order costae, but the spines are almost always broken away when t.he rock matrix is removed, so that their distribution on the juvenile parts of the shell has not yet been observed. The spines in the material at hand are circular in cross section save for an obscure groove along the ventral side, and they are quite solid. A central core of clear calcite extends out on the ventral side to the groove of the spine. The appearance of these spines in section suggests that in life the spines may have had the form of a thick-walled cylinder, split along the ventral side so that the long projection of the mantle within the spine was in contact wit.h the sea water. It is equally possible that the differentiated calcite core represents a final secretion of the mantle, permanently closing the interior of the spine and converting it into a solid structure. The right valve is unknown.

Figure 29Girtypecten sublaqueatus (Girty); upper, juvenile growth stages in a left valve, X 30; lower, cross-section of a spine 3 mm from spine base, X 30 (camera lucida drawings). [Image scaled and magnifications adjusted for web presentation.]

Girtypecten sublaqueatus (Girty).

Comparison—There is no described species known to me that is likely to be confused with this one.

Material—In addition to the holotype (U. S. Geol. Survey, No. 1,211), eight specimens were used in making the description, one hypotype belonging to Yale Univ., Peabody Museum, (No. 14,459), and the other seven belonging to the University of Texas (No. 12,313). The shell substance is altered.

Occurrence—Permian. The species was recorded by Girty from the middle and basal parts of the Capitan formation, Upper Permian, and the Delaware Mountain formation, Middle Permian, western Texas. The hypotypes before me were collected in the Middle Permian Word formation, Glass Mountains, western Texas.

Genus CLAVICOSTA Newell, n. gen.

Orbicular subequivalve, symmetrical, acline, subglobose pectiniform shells, characterized by coarse, nearly identical ornamentation on each valve; coarse, spinose first order costae separated by a pair of smaller intercalate second order costae; auricles subequal, differentiated from the shell body by different ornamentation; spines U -shaped in cross section, arranged more or less regularly in concentric rows.

GenotypeClavicosta echinata Newell, n. sp.

Range— Westerville limestone, Missouri subseries, Pennsylvanian, to the Big Blue series, Lower Permian.

Remarks—This genus is so dissimilar to all other forms with which I am familiar that it is difficult to classify it properly. The hinge structure observed in two individuals is that of the Aviculopectininae. No other known Paleozoic genus shows intercalaries that are added in pairs as in this one. There is no evidence of a prismatic outer ostracum in the right valve in any of my material, in spite of the fact that some of the specimens are rather well preserved. The equal convexity and nearly identical ornamentation on the two valves is unknown elsewhere in the Aviculopectinidae, except perhaps in the genus Deltopecten,


Plate 13, figures 1-5

Subglobose, orbicular shells, with deeply depressed auricles, separated from the shell body by rather deep auricular sulci and well defined, outwardly curved, sub angular umbonal folds; margin of left anterior auricle rounded, indented at the extremity of the sulcus by a shallow sinus, margin of the rear auricles indented by a broad and fairly deep sinus, so that the posterior auricles are acute; auricles costate, with short vaulted projections extending from the costae, particularly those of the anterior auricles; dorsal half of posterior auricles nearly smooth, or with relatively obscure costae; coarse rugose cardinal costae present. Anterior auricular sulci devoid of costae; shell body of both valves with two sets of costae-prominent rounded first order costae with numerous tangential spines arranged in irregular concentric rows, and depressed second order costae as broad as those of the first order, intercalated in pairs between the larger ones; each second order costa on the right valve ornamented with three rows of fine vaulted, erect scaly protuberances, two lateral rows and a median one, the second order costae of the left valve being provided generally with only a median row of such projections extending along the crest of each costa, rarely with three rows; concentric fila lacking, growth lines swing downward between costae as in Acanthopecten, except that they form rounded, instead of pointed, projections.

Material—The species is based on 13 specimens, all more or less worn and fragmentary, from several localities and horizons. In view of the fact that such a long stratigraphic range is included in the collection, it is possible that additional material will furnish basis for dividing the group into more than one species. The types are Kansas Univ., Paleont. Type Coll., No. 377; Yale Univ., Peabody Mus., Nos. 14,480 (holotype) to 14,483.

Occurrence—Upper Carboniferous and Lower Permian. The holotype and some topoparatypes were found in the lower Eiss limestone (Council Grove group) just west of the cemetery northwest of Strong City, Kan. Other specimens are from the Hughes Creek shale (Council Grove) on the east bank of Cottonwood river, east of Elmdale, Kan.; Crouse limestone (Council Grove), NE sec. 22, T. 34 S., R. 7 E., Cowley county, Kansas; White Cloud shale (?) (classed by Condra as Auburn shale), (Wabaunsee group); Barroum Ranch, Osage county, Okla.; Americus limestone (Council Grove), Elmdale, Kan.; Brownville limestone (Wabaunsee group), 1 mile south of Unadilla, Neb.; one specimen from the Oread formation (Shawnee group), at Snyderville, Neb., seems to be a member of the species.

Fragmental material, probably representing several species, comes from the Westerville limestone (Missouri subseries) , Kansas; Weeping Water limestone (Shawnee group), Nebraska; "South Bend" shale (Virgil subseries), Texas; Saddle Creek limestone (Big Blue series), Texas; Graham formation (Virgil) , Texas; Calhoun shale (Shawnee), Kansas; Topeka formation (Shawnee), Kansas; Biel limestone (Shawnee), Kansas; and Stine shale (Admire group), Kansas.

Measurements of Clavicosta echinata Newell, n. sp.
Umbonal angle Auricular costae Body costae
Maximum At
Anterior Posterior First
L1 a 31 29+   8 110 86   3+ 10+ 20 30+
L2 26± 26.5 18 7 108± 93 8 9 11 20 31
L3 13.5 14.5 10.5 3.5 95 83 8 10 20 30
R4 31 29±   7 105± 95± 4+ 10 21± 31 ±
R5 19 19 14.5 4.5   86 4 2+ 10 19-20 30±
a. The holotype. L, left valve; R, right valve.

Subfamily Streblochondriinae Newell, n. subfamily

Smooth or sculptured opisthocline shells having a relatively broad and long anterior auricle, and a small or obsolete posterior one; ligament area similar to that of Aviculopecten, except that in some of the genera the obliquity of the resilifer is backward; outer ostracum in most genera radial crossed-lamellar in both valves, prismatic structure unknown; inner ostracum concentric crossed-lamellar in some genera; both valves of nearly the same convexity, the right one being only slightly flatter than the left. Figure 17 indicates the inferred phylogeny of the subfamily.

Genus STREBLOCHONDRIA Newell, n. gen.

Streblopteria (part) of authors.

Shell slightly but persistently opisthocline, nearly equivalve, the right valve being slightly flatterespecially over the umbo-than the left; shell ornamented with numerous radiating intercalate costae on both valves, crossed by fine regular fila so that the surface has a regular latticed ornamentation; in some species the ornamentation becomes obsolete across the posterior part of the shell, or across the middle, in others the lattice ornamentation is preserved only at the umbones; resilifer with a marked backward obliquity, most pronounced in young individuals, even at a stage prior to the opisthocline obliquity of the shell, becoming less oblique in large adults, resilifer supported within the umbonal cavity by a buttress extending from middle of the inner surface of the "hinge plate:' to the ridge on the inner surface corresponding to the external anterior auricular sulcus; shell substance in each valve composed of two layers, an outer thin film of radial crossedlamellar calcite, and an inner ostracum of very much finer concentric crossed-lamellar aragonite; anterior auricle about twice as long as the posterior, both auricles having rectangular terminations; umbonal folds rounded, rather poorly defined; auricular sulci very well defined, narrow; surface of auricles above the sulci nearly flat.

Figure 30—Comparison of some American species of Streblochondria, showing relative geologic age, X 0.7. [Image scaled and magnifications adjusted for web presentation.]

Comparison of some American species of Streblochondria, showing relative geologic age.

GenotypeAviculopecten sculptilis Miller, Westervlle oolite, Missouri subseries, Pennsylvanian (Upper Carboniferous), Kansas City, Mo.

Range—Mississippian (Lower Carboniferous) to Permian. It is possible that Upper Devonian species like Aviculopecten cancellatus (Hall) represent the ancestral radicle of Streblochondria.

Measurements in Species of Streblochondria
Species Specimen
at beak
hertzeri L1 30 33   4.5 97 89 73 11
L2 24 28 13.5   96 85 73 12
L3 16 18 9.5 1.5+ 93      
L4 10.5 12 7   94±   56 11
R5 17 20.5     94±   86  
R6 8 10 5+       41
sculptilis L1 41.5 48.5 21 7 87 80 50± 2
L2 9.5 12 80± 80± 42 2-3
R3 a 29 33 17   92 82 70-75 8
R4 10   6   82± 82± 55 7
stantonensis L1 a 33 43.5 17 5 80 73 59 8
L2 27 33 15 4 83 75 58± 5+
L3 37.5 47   6 81 79    
condrai L1 a 15 20 8.5 3.5+ 93 87 40 8
L2 18 22         40  
R3 15   10±   85± 75+ 52 7
guadalupensis L1 a 11 13 7.5   88      
R2 18 20 9.5   93      
tenuilineata L1 10 12 5.6 1 85      
R2 a 14 15 7 2 105      
a. The holotype. L, left valve; R, right valve.


Plate 16, figures 5a-c, 7, 9a, b, 11

Aviculopecten sculptilis Miller, 1891, Ind. Geol. Survey, Adv. sheets, 17th Rept., p. 92, pl. 20, fig. 5. ——, Beede, 1900, Kan. Univ. Geol. Survey, vol. 6, p. 122, pl. 13, figs. 3-3b. ——, Sayre, 1930, Kan. Geol. Survey, Bull. 17, p. 119, pl. 11, figs. 9, 10.

Shell, distinctly higher than long, slightly opisthocline, with a slightly arcuate, rounded anterior umbonal fold and a nearly straight, well defined posterior one; beaks sharp, narrow; maximum umbonal angle in adult about 90 degrees; anterior auricular sulcus narrow, quadrate, so that the flat auricle meets the high inner wall of the sulcus at nearly a right angle; surface exclusive of auricles finely cancellated on both valves by intercalate radiating costellae, crossed by fila of about the same order of size; there are three to four ranks of costellae on a large adult and they are only about 70 percent as numerous on the left as on the right valve; toward the ventral and front margins the fila become lamellose in adult shells and become relatively less prominent than the costellae; at the posterior margin of the shell body, the costellae become narrow and obscure; small scale-like projections occur at the intersections of costellae and fila at a mature stage; rear auricle of both valves nearly smooth save for ordinary growth lines, and on the anterior auricle of the left valve there commonly are two or three faint costellae, crossed only by coarse growth lines; cardinal costae obscure or lacking, except for a large rugose costa on the anterior auricle of the right valve; and there are in addition six to eight closely spaced costellae on the surface of this auricle, the one bounding the byssal notch being commonly somewhat larger than the others, and the costellae are crossed -by regular fila such as those on the shell body; anterior auricle of each valve twice as long as the posterior; terminations of all excepting the anterior right auricle quadrate, the latter being rounded; anterior marginal sinus of the left valve subangular; outer thin ostracum in each valve with radial crossed-lamellar structure; structures of inner ostracum unknown.

Measurements of Streblochondria sculptilis are given in the table previous.

Comparison—This beautiful species is similar to Streblochondria hertzeri (Meek) and S. stantonensis, n. sp. From the former it differs especially in having a smaller umbonal angle, nearly smooth, rather than sculptured auricles, and in having the auricles depressed much farther below the general shell surface. A larger number of costae occur on S. hertzeri. Streblochondria stantonensis is a relatively higher form, with costate left anterior auricle, and almost, but not quite, straight umbonal slopes. Furthermore, the sinus at the margin of the left anterior auricle is rounded instead of angular as it is in S. sculptilis.

Material—Through the kindness of Prof. N. M. Fenneman and Mr. M. S. Chappars of Cincinnati University, I have been enabled to restudy the holotype of S. sculptilis (Cincinnati Univ., No. 3,894). This is a well-preserved right valve, embedded in a white oolite matrix. The locality from which it came is Kansas City. There can be no doubt that the original horizon was the Westerville oolite, because the species is common only at that horizon at Kansas City. In addition, I have a large left valve, the same figured by both Beede and Sayre (Kansas Univ., Paleont. Type Coll., No. 386.1), (Kansas Univ., Paleont. Type Coll., No. 386.3); one small left valve and one small right one (Kansas Univ., Paleont. Type Coll., No. 386.2). All of these are topotypes.

Occurrence—Upper Carboniferous. Kansas City group, Missouri subseries, Pennsylvanian. Several specimens of the species have been found in the oolitic part of the Westerville limestone at and near Kansas City; Drum oolite, cement plant, southeast of Independence, Kan.; lower oolitic bed of the Farley limestone, quarry NW cor. sec. 11, T. 10 S., R. 23 E., Kansas.


Plate 16, figures 6, 10, 12-15

Aviculopecten (Streblopteria?) hertzeri Meek, 1871, Philadelphia Acad. Nat. Sci., Proc., p. 61; 1875, Paleontology, Ohio. vol. 2, p. 330, pl. 19, figs. 13a-c.
Aviculopecten hertzeri Morningstar, 199B, Ohio Geol. Survey, Bull. 25, p. 226, pl. 13, fig. 4 (not fig. 3).

This species is similar to S. sculptilis (Miller) and the two often have been considered synonyms. In fact, they can be distinguished readily by the more numerous costellae on the left front auricle as well as the shell body in S. hertzeri, by the greater umbonal angle, greater proportion of length to height, and ornate auricles of this form. There are 11 or 12 narrow, high costellae on the left anterior auricle, crossed by even higher regular fila that are continuous with those of the shell body. The posterior auricles are without distinct costellae, but they are ornamented by high, narrow fila. The anterior umbonal fold is narrow, rounded, curved outward slightly more than in S. sculptilis, and the rear fold is nearly straight. The anterior sulcus of the left valve is rounded instead of angular, producing a rounded sinus at the edge of the shell. The auricles are not depressed so markedly beneath the general shell surface as in S. sculptilis. Radial crossed-lamellar structure of the outer ostracum is well shown in several specimens, both right and left valve.

Measurements of specimens of Streblochondria hertzeri are given in the table previous.

Comparison—The characters of form and ornamentation of auricles that distinguish this form from S. sculptilis (Miller) have been indicated. From S. stantonensis, this species is easily distinguished by its greater umbonal angle and greater proportion of length to height.

Material—It has not been possible to locate Meek's types of Aviculopecten hertzeri. They were said to have been borrowed from Rev. H. Hertzer of the Ohio Geological Survey, and it is possible that some day they will be recognized in the collections of that institution. Fortunately the approximate locality and horizon of the types are known, so that it is possible to recognize the species. The above description is based on several specimens: an external mold from the McArthur member of the Pottsville formation, Moore mine, Elk Township, Vinton county, Ohio (Ohio St. Univ., No. 15,246); four molds from the lower Mercer limestone, Pottsville, Flint Ridge, Licking county, Ohio (U. S. Nat. Mus., No. 89,790); three other specimens from the same horizon and locality as the last (Kansas Univ., Paleont, Type Coll., No. 387); one squeeze of a right valve from the same place and horizon as the preceding two collections (Yale Univ., Peabody Mus., No. 14,457). Two of the specimens are fine internal molds, showing well the cardinal structures of Streblochondria.

Occurrence—Upper Carboniferous, Des Moines subseries, Pennsylvanian. Meek's types are said to have come from Newark, Ohio, in the Lower Coal Measures. His specimens might have been obtained from either the lower Mercer or McArthur members of the Pottsville formation where the species is said to be abundant (Morningstar, 1922, p. 226). Specimens from both horizons show close agreement. Authentic specimens from the Mid-Continent region do not occur in our collections.


Plate 15, figures 1a, b, 3, 4

Shell high, narrow, with acute beaks; slightly opisthocline, nearly acline; anterior and posterior auricular sulci and corresponding sinuses broadly rounded; anterior fold of the left valve narrow, rounded, curved outward only very slightly; auricles ornamented by irregular growth lines; anterior auricle of the left valve with low, relatively broad costae. Right valve unknown.

Measurements of specimens of S. stantonensis are given in the table previous.

Comparison—This species is distinctive, although at first sight it might be mistaken for S. sculptilis (Miller). It is especially characterized by the small umbonal angle and nearly straight umbonal folds, and by the fact that the left anterior sulcus, although deeply impressed as in S. sculptilis, is rounded and broad instead of angular.

Material—Description of S. stantonensis is based on 12 specimens from a single locality. Most of them are fragments and none are well preserved, but in each instance there is a close correspondence in form, indicating a surprisingly small range in variation. The holotype and topoparatypes are in the Kansas Univ., Paleont. Type Coll., No. 381.

Occurrence—Upper Carboniferous, in arenaceous, cross-bedded, oolitic limestone of the South Bend member of the Stanton formation (Lansing group, Missouri subseries), Pennsylvanian, cement plant quarry, Fredonia, Kan.


Plate 14, figures 6, 7

Aviculopecten? montpelierensis Girty, 1910, U. S. Geol. Survey, Bull. 436, p. 42, pl. 4, figs. 9, 10.

Girty's description:

Shell sometimes attaining a medium or rather large size, subcircular, somewhat longer than wide; axis perpendicular to the hinge which is somewhat shorter than the width below. The convexity of both valves is about the same and rather high for the genus. In the right valve the anterior wing is depressed, sharply defined, auricular, with a deep byssal sinus. The posterior wing is small, narrowly triangular, and much depressed below the body of the shell, which arises abruptly from it. The outline rounds out strongly on the anterior side beneath the ear and to a less degree on the posterior side.
The shape of the left valve is somewhat similar to that of the right, though the anterior wing is not auricular and it has no sinus beneath it. It is more sharply defined than the posterior wing, though both are rather abruptly depressed.
In most specimens the surface of both valves appears to be smooth, with no markings except very obscure growth lines. In a few, however, there are traces of regular closely arranged, concentric lirae. These probably are a eonstant character of the shell and would be seen on all specimens if well preserved. Whether they are confined to the left valve or are common to both valves, however, has not been determined.
The largest specimen referred to here has a length of 33 mm., but the average is much smaller. In some examples the anterior side projects considerably more than the posterior, but usually the axis is about perpendicular to the cardinal line and the two sides are approximately symmetrical. Always, however, the anterior wing is larger and more sharply defined than the posterior. In the left valve the anterior wing often descends abruptly from the general convexity. The depression of the posterior wing is more gradual, but depends on the convexity of the medial portion, which varies in different individuals. The size of the wing is also subject to variation.

In addition it should be noted that there are almost invisible traces of radiating costellae on the umbonal area of the left valve. The concentric ornamentation alluded to above appears to me to be irregular undulations and varices of growth. There are no cardinal or other costae on the right valve. The anterior urn bona I fold slightly overhangs the anterior sulcus in the left valve.

Remarks—It is impossible to determine the affinities of this species from the material at hand. It was provisionally placed here because of the close similarity that it bears to Streblochondria? tenuilineata (Meek and Worthen). There is no reason to believe that this type of shell is one of the Pectinidae, as some of the Europeans have suggested by classing such shells with Pseudamusium or the poorly known Syncyclonema. On the other hand, the extreme simplicity of Carboniferous and Permian shells like the present species makes their discrimination difficult.

Comparison—This form is similar to Streblochondria? tenuilineata, but is more nearly circular and lacks auricular costae. Furthermore, there is no trace in the material at hand of the umbonal fila of tenuilineata.

Material—Two type specimens (U. S. Geol. Survey, Nos. 1,714, 1,713) are the basis for the above comments. I was permitted to study them through the courtesy of Doctor Girty.

Occurrence—Permian, in black, carbonaceous limestone of the Phosphoria formation, Montpelier, Idaho, U. S. Geol. Survey station 3,511, Crawford Mountains, Wyo.; Thomas Fork, Wyo.; Bear Lake, Idaho.


Plate 1, figure 3; Plate 15, figures 10-16

Pecten tenuilineatus MEek and Worthen, 1860, Philadelphia Acad. Nat. Sci., Proc., p. 452.
Streblopteria? tenuilineata Meek and Worthen, 1866, Illinois Geol. Survey, vol. 2, p. 334, pl. 26, figs. 9a, b.
Crenipecten foerstii Herrick, 1887, Denison Univ., Sci. Lab., Bull., vol. 2, p. 28, pl. 3, figs. 9, 9a.
Crenipecten foerstii Mark, 1922, Ohio Geol. Survey, Bull. 25, p. 230, pl. 13, figs. 7, 8.
Streblopteria tenuilineata Sayre, 1930, Kansas Geol. Survey, Bull. 17, p. 121, pl. 11, figs. 3-3a.

Orbicular, slightly opisthocline, essentially smooth shells with the hinge margin about one half as long as the shell, and auricles of subequal length, the anterior only slightly longer than the posterior; valves moderately inflated, the right slightly flatter than the left; auricular sulci poorly defined, so that the angle at which they diverge is indefinite (the angle in the left valve at hand is approximately 85 degrees); shell body of the left valve smooth in the later stages, save for obscure growth lines, but covering the umbo to a shell height of about 3 mm. surface ornamented by relatively broad, flat and obscure fila separated by very narrow, sharply depressed interspaces; fila very uniform, increasing very gradually outward from the beak; along the vertical axis at a shell height of 2 to 3 mm., 18 fila occur in a space of 1 mm.; fila intersected by exceedingly fine, numerous costellae, producing a cancellated ornamentation that is scarcely visible without considerable magnification; costellae somewhat finer and more obscure than the fila, and distally fainter until there is no trace of them beyond a shell height. of 2.5 mm.; depressions or pits occurring between the intersections of fila and costellae start to fade out so that the shell appears punctate over a small area; in addition to these juvenile characters the left valve shows a few faint, poorly defined radiating undulations. The auricles are set off by sulci, anterior fairly well defined and narrow, posterior broad, poorly defined; front margin of the flattened anterior auricle broadly sigmoid, with a broad and shallow byssal sinus below and a broad crest at the upper part of the anterior margin of the auricle; outer edge of the auricle meets the cardinal margin obliquely in a continuation of the marginal crest, but in juvenile stages, as shown by growth lines, there is a narrow, poorly defined sinus between the crest. and cardinal margin, so that. growth lines are somewhat recurved from the crest, intersecting the cardinal margin almost at right angles; posterior auricle only very slightly shorter than the anterior, but its area is very much less because the posterior umbonal slope curves inward, encroaching on the area of the auricle, whereas the anterior umbonal slope curves outward, giving the inner border of the anterior auricle a convex outline. The nearly straight dorsal part of the posterior margin of this valve meets the cardinal margin at an angle of about 130 degrees.

Figure 31Streblochondria? tenuilineata. Early growth stages in a paratype, showing progressive changes in form; camera lucida drawing of growth varices at shell height of 2.1 mm., 3.3 mm., and 5.0 mm., respectively.

Streblochondria? tenuilineata. Early growth stages in a paratype, showing progressive changes in form.

The holotype, a right valve, has a clearly defined groove corresponding to the trace of the byssal notch, but the posterior sulcus is poorly defined. The umbonal angle approximates 105 degrees as a maximum, and about 85 degrees at the beak. A projection of the nearly straight dorsal part of the posterior margin meets the cardinal margin at about 130 degrees, but the posterior margin curves abruptly outward just under the hinge line, so that the angle is only a little greater than 90 degrees.

The body of the shell is smooth except for irregular fine growth lines in the adult parts of the shell and fine fila or regular growth lines on the slopes of the beak. The beak is slightly worn on this valve, as is generally the case in right valves, but apparently the ornamentation of this part of the shell was similar, although much finer than that of the left valve. Traces of obscure, irregularly spaced furrows radiate across the body of the shell from the beak. These are very narrow and can be seen only by proper illumination.

The anterior auricle is set off from the shell body by a narrow and deeply impressed sulcus which terminates distally at a narrow, sharply angular byssal notch. The anterior margin of this auricle is almost semicircular except for three slight crests corresponding to three narrow and shallow radiating sulci. The three sulci divide the auricle into four subequal areas. The cardinal and inner margins of the anterior auricle diverge from the beak at about 53 degrees in the adult, but the angle is larger at younger stages because of the outward flare of the anterior umbonal slope. The anterior auricle is ornamented by coarse irregular fila separated by shallow interspaces of about the same width as the fila. Up to a length (measured from the beak along the cardinal margin) of about 1 mm., the ornamentation is conspicuously finer than at later stages. This rather well-marked change occurs when the shell is about 4 mm. high. The fila extend dorsally beyond the cardinal margin in such a manner as to produce a regularly denticulate margin. There are 11 or 12 of these denticles on the anterior auricle of the holotype; about 5 denticles occupy the space of 1 mm. The relatively finer surface of the juvenile part of the auricle lacks welldefined projection at the cardinal margin, but after they appear, the spacing appears to be fairly uniform.

The posterior auricle is not arched dorsoventrally like the anterior one, but is nearly flat, and is set off from the umbo by an ill-defined sulcus. This sulcus is not depressed below the general surface of the auricle but nearly represents the indefinite juncture of the flat auricle and the convex umbonal slope. Because of the prosogyrate curvature of the umbo, the area of this auricle is less than it would be if the umbo were not curved. The posterior auricle is slightly shorter than the anterior, in a ratio of about 3/4. The surface of the auricle is ornamented by two obscure, narrow sulci and several much fainter ones. At regular intervals along the cardinal margin the growth lines are gathered into angular fila which are abrupt on the posterior side and gentle on the anterior slope, like escarpments of gently dipping sedimentary beds. These fila extend dorsally beyond the main part of the auricle to form 10 or more acute denticles that are spaced about 10 in 2 mm. The fila and denticles are lacking in the juvenile shell near the beak. With the aid of xylol the radiating crossed-lamellar structure of the outer ostracum is readily seen in both valves.

Topotype specimens of Herrick's Crenipecten foerstii from Flint Ridge, Ohio, have been compared directly with the types of S. tenuilineata and there can be no doubt that they are the same. It was possible to examine the hinge in the specimens from Flint Ridge, and the character of the ligament area and resilifer appears to be the same as in Streblochondria sculptilis (Miller).

Measurements of S. tenuilineata are given in the table previous.

Comparison—This shell differs from typical Streblochondria in being mostly smooth, in having a relatively long posterior auricle, and in the rounded, rather than angular left anterior auricle. The only reason indeed, for classifying it with the present genus instead of Streblopteria or similar forms is the cancellated ornamentation of the beaks. The character of the hinge is not even remotely like that of Crenipecten or the true pectinid Pseudamusium, as some of the European writers have classified such shells. Herrick was probably influenced in assigning this form to Crenipecten by the denticulate ornamentation of the dorsal margin in the right valve.

Material—The original types of Streblochondria? tenuilineata (Univ. Ill., No. 12,880) were generously secured for me by Dr. J. Marvin Weller. The holotype is an exquisitely preserved right valve, and the topoparatype is a smaller, incomplete left. valve, adherent to the same rock fragment as the holotype. Herrick's type of Crenipecten foerstii apparently has been destroyed, but I have examined several topotypes from Flint Ridge. Three of them, possibly paratypes, because they were in Herrick's possession when the species was described, are at the U. S. National Museum (No. 89,789). Other specimens from the same locality are in the Kansas Univ. Paleont, Type Coll. (No. 384). Other specimens of Crenipecten foerstii, described by Morningstar, (Ohio St. Univ., Nos. 15,288, 15,299) were examined, through the courtesy of Dr. J. E. Carman. There is some question as to the proper identification of these latter specimens because they do not conform well in shape to the Flint Ridge material.

Occurrence—Upper Carboniferous. The types are said to have been found in the "Upper Coal Measures," south line of Clinton county, Illinois. A label accompanying the specimens bears the notation "L 86 t." Regarding this locality Dr. Harold Wanless writes, "the horizon here is probably our Shoal Creek limestone, which I believe is equivalent to your Hertha (lower Missouri subseries) or nearly so." The Flint Ridge material is from the lower Mercer limestone, Pottsville, lower Pennsylvanian, Licking county and southeast of Frazeysburg, Muskingum county, Ohio. Typical specimens occur in the black Hushpuckney shale, Swope formation, Devil's Backbone, near Winterset, Iowa. These horizons range in age from early Des Moines to Missouri in the Pennsylvanian series.


Plate 15, figures 6, 7

Aviculopecten guadalupensis Girty, 1908, U. S. Geol. Survey, Prof. Paper 58, p. 436, pl. 16, figs. 20, 20a.
Aviculopecten sp. a Girty, 1908, U. S. Geol. Survey, Prof. Paper 58, p. 436, pl. 16, fig. 21.

Shell markedly opisthocline, anterior auricle about twice as long as the posterior; ornamentation of left valve consisting of coarse, intercalate costae, 23 on the shell body, in two or possibly three ranks, and 4 on the anterior auricle, at least one being a first order costa and the others second order costae; there appears to be in addition an obscure cardinal costa; anterior auricle with a few irregular coarse fila which might appear lamellose in unworn material; anterior sulcus of left valve deep, and there is no overhang of the adjoining fold, the outer slope of the fold being less than perpendicular to the plane of the auricle; posterior sulcus narrow, separating the flattened auricle from the broadly rounded umbo; terminations of the auricles quadrate, except in the front auricle of the right valve which is broadly rounded; ornamentation of the right valve consisting of 29 rounded prominent bifurcate costae and three additional costae on the upper part of the anterior auricle; shell structure not discernible.

Measurements of the types of S. guadalupensis are given in the table previous.

Comparison—This species is unlike any described form known to me, and there is no established genus that includes a shell like this having bifurcate costae on the right valve. On the other hand, the material is much too poorly preserved to warrant erection of a new genus. There can be no question that this is a member of the Streblochondriinae, so that its general relations at least are definitely known.

Material—Doctor Girty has very kindly invited me to examine his type specimens of this as well as other species. Holotype, U. S. Geol. Survey, No. 424; the other figured specimen is No. 425.

Occurrence—Middle Permian. "Dark limestone," Bone Canyon limestone, Pine Spring, Guadalupe Mountains, Tex. (U. S. Geol. Survey sta. 2,930) .


Plate 15, figures 17, 18

Aviculopecten infelix Girty, 1908, U. S. Geol. Survey, Prof. Paper 58, p. 438, pl. 9, figs. 9, 10.

Girty's description:

Shell small, length greater than breadth, erect or slightly inclined backward, cardinal line short. Ears nearly equal, quadrate, or somewhat extended. They are defined by reentrant angles on the outline and by grooves on the surface. The groove defining the anterior ear is more marked than that of the posterior. While without the deep byssal notch and specialized configuration of the anterior ear which is found in some species, the one ear is considerably more sharply defined than the other, and on this account I have regarded it as being; the anterior ear of the right valve. The convexity is low. The inferior margin is broadly rounded.
Except for indistinct concentric markings, the surface is plain, without radiating ribs on any position.

The material on which this species is based, consisting of right valves, is too poor to be certain of the original shell surface. If there was originally any ornamentation, it is now lost from the type specimens. Altogether it seems probable that this species is congeneric with Streblochondria? tenuilineata (Meek and Worthen) and S.? montpelierensis (Girty), this relationship cannot be determined beyond question. It is possible that a left valve of the present species would appear slightly more opisthocline than the nearly acline right valves at hand. Euchondria cannot be considered here, because in that genus the rear auricle is extended, and there is a pronounced prosocline obliquity in all of the known species.

Comparison—From S.? tenuilineata and S.? montpelierensis the present form may be distinguished by its shape, being relatively higher.

Material—The types (U. S. Geol. Survey, Nos. 414, 415), are poorly preserved right valves.

Occurrence—Upper Permian, middle part of the Capitan limestone, Capitan Peak (U. S. Geol. Survey loco 2,926) Guadalupe Mountains, Tex.


Plate 15, figures 8, 9

Slightly opisthocline, high streblochondrias, characterized by a relatively small number of fine, widely spaced radial costellae on the shell body and anterior auricle of the left valve; concentric fila, normal for the genus, replaced gradually at a shell height of about. 7 mm. by irregularly spaced edges of imbricating lamellae, which are flat between costellae but become vaulted over them into small erect projections; auricles flattened, depressed markedly below the general shell surface, separated from the shell body by rather narrow rounded sulci, the inner slope of the left anterior sulcus being nearly perpendicular to the surface of the auricle; left anterior umbonal fold narrow, rounded distinctly, curved outward, posterior one obscure, nearly straight; auricles without distinct regular fila, except for obscure ones on the right anterior auricle; cardinal margins rugose; the rather marked curvature of the anterior umbonal folds suggests that these small forms are nearly full grown. In one left valve there are two or three costellae on the rear auricle, but some other specimens lack them.

Measurements of the types of S. condrai are given in the table previous.

Comparison—The most distinctive thing about this form is the very slender, relatively wide-spaced costellae, which in the mature stage are not crossed by distinct fila. The specimens that I have, although rather small, are apparently mature, as evidenced by the marked curvature of the anterior umbonal folds, and the character of the ornamentation near the border of the shell.

Material—There are six more or less fragmentary specimens in the collection before me. These exhibit such close agreement in size and distinctive ornamentation that it has seemed desirable to describe a new species on them. The inner ostracum has been dissolved from the specimens, but the outer film of ostracum, showing the radial crossed-lamellar structure, is still present in both valves. The holotype and five topotypes are catalogued as Yale Univ., Peabody Mus., No. 14,476.

Occurrence—Upper Carboniferous, in arenaceous and shaly, gray to buff limestone of the Auburn shale (Wabaunsee group, Virgil subseries), Pennsylvanian series, Barroum Ranch, about 7.5 miles northeast of Foraker, Okla.


Plate 15, figure 5

A curious Streblochondria was found near Bartlesville, Okla., in the butte just west of town. This form is distinguished from the others by a very marked opisthocline obliquity and by an obsolescent character of the costellae over the posterior half of the shell. The horizon at Bartlesville is in the Lansing or Pedee group, Missouri subseries. A similar form is not uncommon at the Kereford limestone (Shawnee group, Virgil subseries) near Nehawka and Snyderville, Neb. Unfortunately, the material at hand is too fragmentary to warrant the application of a new name, or even to be positive that all of the several specimens are conspecific. The figured specimen is a squeeze of a fairly well-preserved mold from Bartlesville.


Plate 15, figure 2

Aviculopecten subequivalva Beede, 1902, Kansas Univ., Sci. Bull., vol. 1, p. 149, pl. 5, figs. 3, 3a.

Beede's description:

Shell thick, moderately large, subequivalvular, rather convex, quite oblique, ears well developed. The hinge is nearly straight, the beak does not project, the angle of divergence of its sides is about eighty to ninety degrees. The left valve, exclusive of the ears, is ovate; anterior ear well developed, obtusely angular, marked only by strong lines of growth; the rise from the ear to the body of the shell is abrupt; the marginal sinus separating the ear from the rest of the shell broad; shallow, and ill-defined. The posterior ear is unknown. The anterior margin below the ear forms an ovate curve, which is probably continued on the ventral and marked only by stronger and fainter concentric lines except on the front and back sides, where there are radiating rows of vaulted lamellae. It is entirely probable that these marks once extended over the entire surface, but have been worn off from the more convex portions. Judging from another specimen, the right valve is somewhat flatter than the left and quite as oblique. Posterior ear very small and obtuse; anterior ear quite large, marked by obscure, large radiating ribs and probably vaulted lamellae, as well as strong concentric markings; separated from the shell by a deep sulcus. Margin from the beak around the posterior to near the middle of the shell is a regular ovate curve, anter-ventral margin somewhat produced but rounded, extending obliquely toward the beak until the deep byssal sinus is reached. Ornamentation as in the other valve. In this specimen it seems that the radiating rows of scales covered the entire surface before being worn away. Length, 36 mm.; height, 32 mm.; hinge, 17 mm.; thickness, about 5 mm.
Position and locality: Thin limestone, south of Dover, Kan., in Upper Coal Measures. Type in author's collection.

It appears to me that Beede's description and illustrations do not distinguish this form sufficiently to permit recognition of the species. However, topotype specimens may be secured at some future date, serving as a basis for a revised description.

The rocks in the vicinity of Dover, Kan., belong mostly to the Wabaunsee group (Virgil subseries) of the upper Pennsylvanian.


Streblopteria McCoy, 1851, Annals Mag. Nat. History, vol. 7, p. 170.
Eumicrotis HIND, 1903, Carbo Lamell., vol. 2, p. 43.

Shell acline to opisthocline, orbicular, valves of nearly equal convexity; smooth, with gibbous umbones; posterior umbonal fold lacking in either valve, anterior fold rounded, ill-defined; posterior auricular sulcus broad, coextensive with the poorly defined auricle. anterior sulcus of the left valve narrow, deep, rounded, curving outward markedly; anterior auricle well defined, small, with a rounded anterior margin; posterior auricle ill defined with obtuse terminal angle, as long or longer than the anterior.

GenolectotypeStreblopteria laevigata (McCoy) , Carboniferous limestone, Ireland. Designated by Meek and Worthen (1866, p. 333) and By S. A. Miller (1889, p. 514).

Range—Lower Carboniferous to Permian (?).

Remarks—Our knowledge of the genus Streb lopteria is most unsatisfactory. McCoy described the hinge as having "one short narrow tooth slightly diverging from the hinge line in the posterior side of the beaks; ligament confined to a narrow, simple facet on the hinge-margin." These features of the articulus described by McCoy were not illustrated by him, or by any subsequent writer, so that we are left to interpret as best we can his almost unintelligible statement. No species known to me has the characters mentioned by McCoy.

An extended attempt has been made to secure authentic specimens of Streblopteria laevigata in order to examine and redescribe the hinge structure, but thus far it has not been possible to obtain such specimens. American Pennsylvanian rocks contain a small form that externally is like S. laevigata, and I believe that the two are congeneric. In the American form, Streblopteria oklahomensis, n. sp., I have not been able to make a wholly satisfactory study of the hinge, since the exact shape of the resilifer has not been determined. On the other hand, there is no question that the Pennsylvanian species has hinge structure like those of the Aviculopectinidae. This species is unlike any of the other Streblochondriinae in being devoid of any ornamentation at any stage, and apparently, in having a structureless outer ostracum in both valves.

Whatever may be the hinge characters of Streblopteria, it is absurd to believe that they diverge as greatly from the other Aviculopectinidae as McCoy's diagnosis would suggest. It generally is difficult to see the hinge structures in Paleozoic pectinoids, and it seems highly probable that McCoy mistook the ventral projecting shoulder of the ligament area for a lateral tooth. His failure to recognize a resilifer in Streblopteria is not surprising when we recall that he made such erroneous observation for Aviculopecten. As was pointed out elsewhere, the absence of resilifer pits in shells like this, except in the hinge type possessed by the Pterinopectinidae, would be an anomalous feature, quite incompatible with any of the modern groups that might conceivably be related to the ancient pectinoids, Even in Pinna and Pteria there is a special elongate triangular groove for the reception of the resilium, whereas the non fibrous ligament in front and behind the resilium is not inserted in such a groove, but is confined to a flattened area on either valve.

Hind (1903, p. 43, 47) has confused the issue greatly. He supposed that Meek's Eumicrotis (type Pseudomonotis hawni) was a smooth, biconvex shell. Accordingly, he placed De Koninck's genus Rutotia in synonomy with Eumicrotis. Hind's classification of Eumicrotis and Rutotia, as far as I can tell from the literature, does not differ materially from Streblopteria. In spite of the similarity, amounting almost to identity, between Hind's descriptions and illustrations of Streblopteria and Eumicrotis, he apparently considered the two groups, as classified by him, entirely distinct.

The genus Rutotia as classed by De Koninck (Mus. royale histoire nat. Belgique Ann., tome 11, p. 196) is a smooth suborbicular shell, with poorly defined rear auricles, resembling Streblopteria in most respects but lacking, according to De Koninck's figures, a byssal notch in either valve, and possessing a marked prosocline obliquity. If De Koninck's interpretation of his material was correct, Rutotia is not a member of the Pectinacea.

According to Hind, Rutotia hemisphaerica (Phillips) has a well-defined byssal notch. This species, one of the genosyntypes of Rutotia, as described on authentic material by Hind, looks like a Streblopteria. De Koninck's Rutotia grandis, another genosyntype of Rutotia, looks so different from any other genus that I am disposed to think that someone familiar with De Koninck's specimens should designate it as the genolectotype, if it really has the characters ascribed to it by De Koninck. However, if Rutotia cannot be made known more fully, apparently it could be placed in synonymy with Streblopteria by designating Phillip's Pecten hemisphaericus as the type. It seems unwise to follow either course at the present time, since I have no knowledge of the location or condition of the types, nor any assurance that either De Koninck's or Hind's descriptions are satisfactory.


Plate 14, figures 8a-12

Orbicular, acline or slightly opisthocline, smooth shells, with equally convex, gibbous valves; hinge margin about half as long as the shell length; anterior auricle equal or sligthly shorter than posterior, which is a simple undifferentiated flattening from the umbones, terminating in a definite obtuse angle of a bout 140 to 145 degrees; posterior umbonal fold lacking, sulcus broad, ill-defined, corresponding in area to the auricle; anterior fold distinct, rounded, curving rather markedly outward, bounding on the left valve a deep, narrow sulcus; byssal notch on the right valve ornamented by rugose irregular growth-lines, conforming to the semicircular anterior margin, crossed in some specimens by two or three faint radial grooves, which divide the auricle, so to speak, into three or four broad obscure costae, —— radial ornamentation in other specimens, however, being absent. Thin sections of the shells at hand indicate that the outer ostracum in each valve is homogeneous. Such evidence might at the present time be taken as tentative until other specimens, preserved differently, can be discovered. This outer ostracum of the right valve was definitely not prismatic, however, because species of Aviculopecten and Limipecten having the same clay-ironstone kind of matrix have perfectly preserved polygonal prisms in the right valve. One specimen, an internal mold, shows definitely the divergent ligament area of the Aviculopectinidae. It appears, although this is not certain, that the resilifer is long—one third as long as the hinge margin—and most of it lies behind the beaks. There is no cardinal costa on either valve.

Measurements of Bivalve Specimens of Streblopteria oklahomensis Newell, n. sp.
Specimen No. Length,
of both
1 a 17± 17 7
2 15 16 7.5
3 19 21 9.5 10±
4 15 19 8.5 8
a. Holotype

Comparison—This species is similar to Streblochondria? tenuilineata (Meek and Worthen), but it seems proper to place these species in different genera on the basis of umbonal ornamentation, which is present in tenuilineata and absent in oklahomensis. Our specimens of Streblopteria oklahomensis show the outer ostracum apparently perfectly preserved and unworn, yet there is no discernible ornamentation other than ordinary growth lines, nor is there any visible distinctive shell structure in either valve. Right valves of the two species can be readily distinguished by the peculiar ridge or costa bounding the inner margin of the byssal notch in S. oklahomensis. The size of the angle between the posterior margin of the shell and the hinge line is slightly greater in the present species than in S.? tenuilineata. I am quite confident that the reticulose ornamentation seen on the beaks of tenuilineata would be visible on the present specimens if it ever occurred, because it is readily distinguished in somewhat worn or crushed specimens of the former species, and the specimens of oklahomensis at hand appear to be quite unworn.

Material—The species is based on 10 specimens, well preserved but more or less fragmentary, in every instance with both valves fixed in apposition. Holotype and six topoparatypes, Kansas Univ., Paleont. Type Coll., No. 380; topoparatypes, Yale Univ., Peabody Mus., No. 14,477; and one paratype, Kansas Univ., Paleont. Type Coll., No. 381. All of the specimens are free individuals, from argillaceous gray or buff shale. The interiors contain an exceedingly hard, tough, clay-ironstone matrix.

Occurrence—Upper Carboniferous. A single paratype was collected in the Boggy shale (Des Moines), sec. 18, T. 35 S., R. 7 E., Oklahoma; the other specimens are from a horizon correlated with the basal Eudora shale (Lansing), 2 1/2 miles west of Wann, Okla., and five miles northeast of Copan, Okla.

Genus OBLIQUIPECTEN Hind, 1903

Obliquipecten HIND, 1903, Carboniferous Lamellibranchiata, vol. 2, Palaeont. Soc., p. 114.

Markedly opisthocline Aviculopectinidae with flattened valves, nearly smooth save for a few fine radiating costae on the anterior part of each valve and a few coarse fila on the anterior auricle of the right valve; hinge short, about half as long as the shell body; posterior auricle obsolete, very small and obscure, smaller on the right than left valve, with a very obtuse posterodorsal angle; anterior auricle of right valve subcircular, higher than long, projecting above the hinge axis; umbonal convexity in the right valve projected ventrally in a broad ridge that extends from beak to an obscure angularity at the posteroventral margin, sloping abruptly along its course down to the posterior edge of the shell; central and anterior part of right valve peculiarly flat, without an anterior umbonal fold; left valve with a well-developed anterior fold and an obscure posterior one; posterior area of shell body flattened along an axis corresponding to the posterior ridge of the right valve; posteroventral margin subangular as in the right valve; ligament area comparatively narrow, with a triangular resilifer, the posterior part of which is extended; outer ostracum in each valve radially crossed-lamellar, most readily observed on the auricles; cardinal costa absent.

GenotypeObliquipecten laevis Hind, Carboniferous limestone, Settle, England.

Range—Lower Carboniferous.

Remarks—This genus has not been recorded as yet outside of England. The remarkable extent to which the opisthocline obliquity has been carried, and the nearly complete loss of the posterior auricle characterizes this form from all others.

I must acknowledge the very great generosity of the curators at Sedgwick Museum, Cambridge, England, in entrusting to me the types of Obliquipecten laevis Hind, and with their consent I have been able to prepare the ligament area in the holotype. The ligament area proves to be that of the Aviculopectinidae, and the resilifer has a forward obliquity as in Aviculopecten, rather than a backward obliquity as in Streblochondria.

Figure 32—Plan view of part of the ligament area in left valve of the lectotype of Obliquipecten laevis Hind, X 11, showing the oblique resilifer pit; the arrow points toward the anterior end of the shell. [Image scaled and magnifications adjusted for web presentation.]

Plan view of part of the ligament area in left valve of the lectotype of Obliquipecten laevis Hind.

The types of Obliquipecten laevis (see pl. 8, figs. 3-5b) before me are seven in number, six right valves and one left valve, here designated the lectotype. The specimens are preserved in a fine-grained, hard, gray limestone.


Camptonectes Girty, 1908, U. S. Geol. Survey, Prof. Paper 58, p. 432.

I am tentatively following the course adopted by Girty in dealing with a group of Permian pectinoids from western Texas, although it is my opinion that the species under consideration belong to an undescribed genus of the Streblochondriinae. However, since I am unable, in the absence of good material, to discover any characters of the hinge or significant structures of the shell substance by which this group can be placed in the proper family, I would rather not propose a new genus at this time. The statements made by Doctor Girty on this interesting group of Permian forms are quoted:

This title is used for a peculiar group of forms which occurs in abundance in the Capitan formation of the Guadalupian series. Among its distinguishing characteristics the most striking are its forward obliquity, the large anterior and small posterior ear, the lack of definition of the posterior ear, and the surface ornamentation. The latter character proves to be the very variable. It seems to consist primarily of nodes or papillae which are arranged in curved diagonal lines outwardly concave. These nodes, which distinguish t.he surface of C.? papillatus, appear to have been connected with tubules traversing the shell at a strongly acute angle with the surface, and probably were continued outward into spines, which lay nearly flat along the shell in a radial direction.
With this character is probably connected an observation made on a shell related to those under consideration, In this instance the test was seen to be minutely and abundantly punctate, somewhat as in Terebratula or Eumetria. This is the only example in which punctation was observed, and it is on a much finer scale than the tubules in C.? papillatus; but as will later appear, this group shows wide variations in the scale of its ornamentation. Toward the circumference the rows of nodes tend to pass into continuous lirae, a circumstance which connects this species with C.? sculptilis. There the lirae tend to diverge pinnately from a median line, curving outward as they go. In C.? asperatus the two types of surface are more or less combined, but on a greatly reduced scale and with some modifications. Minute tubulous papillae cover the surface, but over the peripheral portions tend to form continuous lirae, which, however, are not in two sets with a pinnate arrangement, but in multiple groups and with a zigzag direction. It is probable with an ornamentation of this type that the punctate shell above referred to is most easily to be compared. Another factor which may be of importance is that on internal molds of the right valve the anterior ear shows obscure traces of radiating ribs, which are not seen on the exterior.
These shells in some respects can be appropriately compared with McCoy's genus Streblopteria. The forward prolongation of the shell is a rather striking character of both, and still further agreement can be traced in the fact that the anterior ear is defined and the posterior undefined. On the other hand, the type species of Streblopteria is smooth, while these Guadalupian shells have the peculiar ornamentation above described. Furthermore. typical Streblopteria has a large posterior and a small anterior ear. This is one of the diagnostic characters mentioned by McCoy. Unfortunately, in the case of Streblopteria, as well as in Camptonectes?, no comparison can be made in the matter' of internal characters.
Camptonectes seems to agree with the Guadalupian forms in having a large, well-defined anterior ear and small, undefined posterior ear. In some species, at least, it has the same forward prolongation. The characteristic external feature of Camptonectes consists, however, in the radiating lines which diverge along a median line. This peculiar type of sculpture is repeated in C.? sculptilis, but the singular surface features of the other Guadalupian forms which are manifestly closely related to C.? sculptilis are unknown in Camptonectes proper. The punctate structure, which can hardly prove an erroneous observation, is altogether an anomalous character. Of the two genera considered, the Guadalupian forms appear to present points of closer similarity with Camptonectes. If the observations recorded here are established by further research, it seems certain, however, that they belong to a genus yet undefined.

It has not been possible for me to confirm Girty's observations on shell structure in any of the type specimens, but I have not. seen very many of these shells, and those that. I have examined are rather badly altered.


Plate 14, figures 4, 5

Camptonectes? papillatus Girty, 1908, U. S. Geol. Survey, Prof. Paper 58, p. 433, pl. 9, figs. 3-3a, 5-5a.

Girty's description:

The type specimen of this species is a left valve, and from it the following description is taken:
Shell small. rather oblique. and inclined forward. Convexity low and broad. hinge line short. Posterior ear probably small and undefined, anterior ear large and defined both by a notch' in the outline and by being sharply depressed below the curvature of the body of the shell. The axis is curved, concave toward the anterior side. The surface is marked with papillae, which increase in size proportionally to the dimensions of the shell. Over the upper half they are small, and the surface appears to be almost smooth. They have a sort of quincunx arrangement such that they tend to form two sets of curved lines intersecting at an acute angle. Their lines are concave toward the anterior and posterior sides of the shell. Their curvature is greatest near the margins, especially near the lateral margins. In this region also the linear arrangement is more strongly marked, and tends to develop into connected ribs. The papillae appear to have been the bases of small spines pointing radially and almost tangential to the surface.
In addition to the type specimen, four other examples have come to hand, all left valves. They are small and more or less imperfect both as to shape and surface ornamentation, and it can not be told with certainty whether they belong here or with C.? sculptilis. The right valve is unknown, though probably among a number of right valves whose surface has been destroyed by exfoliation representatives of this species are found. It is probable that the right valve is the counterpart of the other in surface and configuration.

It appears to me after examining the types that the preservation is such that no satisfactory conclusions as to the original shell structure can be made, although thin sections might aid. The ornamentation appears to be largely confined to a surficial film of calcite, now granular. I cannot confirm the tubular character of the papillae, but certainly some of them suggest vaulted lamellae, as seen in Pseudomonotis. The preservation is such that the growth lines are not sharp and distinct, and it may be that perfect material would show vaulted projections from the edges of imbricating growth lamellae. No evidence of punctae was seen. The auricles appear to have been smooth, but the preservation is not wholly satisfactory in this particular.

Comparison—This species is distinguished from similar ones by the rather coarsely papillate nature of the ornamentation.

Material—Holotype, U. S. Geol. Survey, No. 351, a nearly complete left valve, but preserved rather imperfectly.

Occurrence—Upper Permian, middle Capitan limestone, Capitan Peak (U. S. Geol. Survey sta, 2,926) Guadalupe Mountains, Tex.


Plate 14, figure 1

Camptonectes? sculptilis Girty, 1908, U. S. Geol. Survey, Prof. Paper 58, p. 434, pl. 9, figs. 4, 4a.

The ornamentation consists of "two sets of curved lirae apparently developed pinnately along the median line" rather than the rows of papillae such as occur in C.? papillatus.

The holotype is a fragment of a right valve, showing well the surface ornamentation, but illustrating very little else.

Comparison—This form is distinct from similar ones in the character of ornamentation. Other means by which it might be distinguished from species having the same type of ornamentation must await discovery of more complete material.

Material—Holotype, a fragmentary right valve, U. S. Geol. Survey, No. 352.

Occurrence—Upper Permian, middle Capitan limestone, Capitan Peak, Guadalupe Mountains, Tex. (U. S. Geol. Survey sta. 2,926); questionably identified in the Word formation of the Glass Mountains, 1.5 mile N. 55 degrees W. of the old Hess ranch house, western Texas.


Plate 14, figures 2, 3

Camptonectes? asperatus Girty, 1908, U. S. Geol. Survey, Prof. Paper 58, p. 434, pl. 9, figs. 1, 2.

Girty's description:

This species much resembles Camptonectes? papillatus, the chief difference being in the surface ornamentation. The shape appears to be almost identically the same, but as the typical examples are right valves there is a deep notch under the anterior ear. The surface is of the same character as C.? papillatus, but on a very much finer scale. Apparently two types of surface are found to occur on the same shell. one consisting of intersecting rows of papillae and the other of intersecting lirae. I am inclined to believe that the two kinds of surface are more or less alternating. The scale is so small in the case of this species that it is difficult to tell whether the lines are continuous or interrupted; and it seems probable that preservation might alter the appearance to some degree. The lines have a more or less zigzag appearance on a portion of the surface.
All of these specimens are right valves, and as they occur in the same beds with C.? papillatus, which is represented by left valves, the presumptive evidence is certainly considerable that they belong together. On the other hand, the surface ornamentation though of the same general character as in C.? papillatus is yet so different in effect that the greater probability seems to favor regarding them as distinct. Furthermore, in C.? sculptilis both valves seem to have the same and not different ornamentation, though this fact, which would be important if proved, cannot be insisted on, because some uncertainty exists as to whether all the shells referred to sculptilis really are of the same species.
The fossils representing these species indicate that the two valves are practically equal, and that they have similar if not the same surface ornamentation.

Comparison—The distinguishing features of the species have been stated in the above description.

Material—The holotype (U. S. Geol. Survey, No. 355) and one other type specimen (U. S. Geol. Survey, No. 354) were examined through the kindness of Doctor Girty. These specimens are somewhat better preserved than is commonly the case in the group.

Occurrence—Upper Permian, middle Capitan formation, Capitan Peak, Guadalupe Mountains, Texas (U. S. Geol. Survey sta. 2,926); also questionably identified from the Word formation, Glass Mountains, 1.5 miles N. 55 degrees W. of the old Hess Ranch House, western Texas.

Subfamily Pseudomonotinae Newell, n. subfamily

Aviculopectinidae having a nearly flat or concave right valve, a very convex left valve, and retaining a primitive prosocline rhombic form until a relatively advanced ontogenetic stage; posterior auricle not extended nor set off from the shell body by a marginal sinus; retractors lost in sessile forms; right outer ostracum irregularly prismatic; left outer ostracum structureless, Figure 17 indicates the inferred relationships.

Genus PSEUDOMONOTIS Beyrich, 1862

Pseudomonotis E. Beyrich, 1862, Zeitschr. d. deutsch. geol. Gesell. Bd. 14, S. 10; genolectotype, Gryphites speluncaria Schlotheim, from the German Zechstein, selected by Stoliczka (Geol. Survey India, p. 389, 1871).
Eumicrotis Meek, 1864, Am. Jour. Sci. 2d ser., vol. 37, p. 216; genoholotype, M onoiis hawni Meek and Hayden, from Big Blue series of Kansas.
Prospondylus Zimmermann, 1886, Jahrb. d. h. preuss, geol. Land., S. 109; genoholotype, Prospondylus liebeanus Zimmerman, from the German Zechstein.
Aviculomonotis Grabau, 1931, Nat. Hist. Central Asia, vol. 4 Permian of Mongolia, p. 322; genoholotype, Aviculomonotis mongoliensis Grabau. from the Permian Jisu Honguer limestone of Mongolia.

In addition to the family and subfamily characters, the genus is characterized by simple costate ornamentation on both valves, increase in ornamentation being by implantation; right valve attached at the umbo to extraneous objects throughout life, or only during maturity; retractor muscles obsolete in adults, correlative with an invariably obsolescent or obsolete byssal notch. The outer ostracum of the right valve is irregularly prismatic calcite exactly as in Aviculopecten, the left, homogeneous calcite; inner ostracum aragonite, microstructure unknown; in most species the shell passes through a curious cycle of form changes, beginning with the primitive prosocline shape, passing through acline and opisthocline form stages respectively, and finally reverting at full maturity to a secondarily acquired prosocline obliquity.

Remarks—Great confusion has long existed regarding the nature of Pseudomonotis, most of the difficulty arising from lack of agreement as to the genotype species. One modern school, following M. Cossmann (1902, p. 75,194), has accepted Gryphites speluncaria Schlotheim of the Zechstein as the genotype. A second school, under the leadership of C. Diener (1902, p. 342; 1903, p. 17; 1923, p. 35), regards the Triassic form, Avicula ochotica Keyserling, as the type species of Pseudomonotis. In my opinion, as well as that of some other paleontologists, the Zechstein and Triassic species are not congeneric, and therefore the issue should receive a solution that may be accepted by all.

Pseudomonotis was established by Beyrich in 1862 as a subgenus of Avicula. The following is a free translation of the reference from which Pseudomonotis must date:

The second species from L. von Buch's collection from Schwerfen, near Kommern, is similar to Avicula contorta of the Kessen beds, but the preservation prevents a complete comparison. A. contorta is not a Cassianella, although the associated beautiful Avicula speciosa of the Alps belongs to this genus. A. contorta belongs in the group of inequivalve Avicula species which begins with the Zechstein Avicula speluncaria and is frequently quite erroneously classified with Bronn's Monotis. The Monotis (type M. salinaria) is almost equivalve, without a byssal ear. The inequivalve true Aviculae of the indicated affinities can be named as a subgenus Pseudomonotis, to which Aucella might be related by virtue of the reduction of the posterior ear as compared to the characteristic Avicula form. (Beyrich, 1862, p. 10.)

According to legal procedure Avicula contorta Portlock, from the Rhaetic beds, and Avicula speluncaria (Schlotheim) from the Zechstein, are the genosyntypes, and the subsequent designation of a genolectotype for Pseudomonotis, in order to be valid under the code of International Zoological Nomenclature, must apply to one of these two species, and no other.

In 1871, Stoliczka (1871, p. 389) designated Gryphites speluncaria Schlotheim as genolectotype for Pseudomonotis, and as far as I can learn this was the first published selection of a type for the genus.

The selection of Avicula ochotica Keyserling by Diener as the type of Pseudomonotis violates the rules, which provide that only those species listed in the original reference to the genus, and which fall within the generic diagnosis are to be considered in the selection of a genolectotype.

In 1864, Meek (1864, p. 216) proposed the new genus Eumicrotis, with the genotype Monotis hawni Meek and Hayden, recognizing the close relationship of M. hawni and Monotis speluncaria (Schlotheim). As soon as Meek learned that his genus was antedated by Pseudomonotis Beyrich by two years, he immediately and properly abandoned Eumicrotis for the former genus.

In 1903. Hind (1903, p. 43) proposed to distinguish Eumicrotis from Pseudomonotis on the grounds that Eumicrotis, as exemplified by E. hawni, was thought to be less convex than the genotype of Pseudomonotis, P. speluncaria, and to lack the peculiar posterior lobe separated from the remainder of the shell by an oblique sulcus on the left valve. Unfortunately, Hind completely misinterpreted the nature of E. hawni, for he applied the term Eumicrotis to British Lower Carboniferous smooth forms that probably should be classed as Streblopteria.

The lobation referred to by Hind is not useful, even as a specific character, because it is encountered in almost every known species of Pseudomonotis s. s. The lobation is not a constant feature of any species known to me, because many specimens exhibit no trace of lobation, but are associated with lobed specimens which in other respects they resemble.

Many kinds of pelecypods exhibit a lobation like that shown in some Pseudomonotis. Regarding the origin of the posterior lobation in oysters Jackson (1890, p. 307) says:

The sinuosity of the right valve is apparently due to the constantly retracted condition of the right mantle border at this point. It is constantly retracted to admit of the passage of the excurrent water and being so retracted, as a necessary result, the shell is not built at this area as rapidly as at other places where the mantle is fully extended. It might be considered that the peculiar excurrent opening was due to the mechanical conditions under which the oyster lives, an opening being necessary on account of the close relation of the shell to the object of fixation, and it is possible that this is the case; but against it may be urged the fact that no such character is found in Anomia which is subject to similar conditions. I think that this excurrent passage and the correlated sinuosity of the right valve are of hereditary significance. Examining the fossils, we find a similar sinuosity of the left and right valve characteristic in marked degree of the genus Gryphaea; it is also found frequently in Exogyra and in many fossil members of the Aviculidae, from which last group the Ostreidae were doubtless evolved.

I am inclined at the present time to take exception to the last suggestion concerning the possible derivation of the oysters from the pterioids (or pectinoids). Oysters are invariably attached by the left valve, whereas all pterioids and pectinoids lie on, or attached by the right valve. Furthermore, there is no byssal notch at any stage in any of the oysters. In spite of the striking resemblance of form and ligament between Gryphaea and Pseudomonotis there appears to be little liklihood that they were closely related.

Further controversies regarding Pseudomonotis center around the genus Prospondylus, established in 1886 by Zimmerman on the basis of the Zechstein Prospondylus liebeanus Zimmermann (1886, p. 109). At present I have no original observations regarding Prospondylus because authentic representatives of P. liebeanus have not been available to me. The problem is well summed up by Licharew (1931, p. 35) who states that:

Prospondylus was placed by Zimmerman between the Spondylidae and Pectinidae. Frech in 1891 identified it with Hinnites. Netchaev referred Prospondylus to the Ostreidae, but in 1898 Philippi again considered it as a representative of the group of edentulous Spondylidae and gave it the following diagnosis: "Formen mit massig breiter, Austernähnlicher Ligamentgrube, die linke Klappe meist tiefer als die rechte. Vorn und hinten deutlich ausgebildete Ohren. Skulptur besteht aus dichtstehenden Rippen erster und zweiter Ordnung. Zechstein-Deutsche Trias."
In 1912 Frech returned to the question of Prospondylus. Having discovered the presence of a notch for the issue of byssus in the anterior auricle of one of the specimens of this form from the Zechstein of Murom, determined by him as Prospondylus liebeanus Frech, he concluded that Prospondylus is to be considered as a subgenus of Pseudomonotis sensu lato. He gives the following diagnosis of Prospondylus: "Wölbung der beiden kraftigen Schalen annähernd gleich; die recht festgewachsene Klappe ein wenig konvexer, als die linke. Byssusohr sehr deutlich abgegrenzt. Radialskulptur kraftig. Ligamentgrube subcentral, gross."
According to Frech, Prospondylus differs from Pseudomonotis sensu lato in a sharply pronounced ornamentation, a greater thickness of the attached valve and a backwardly inclined ligament. Besides Prospondylus liebeanus Zimmerman, Frech refers to this genus five other species from the Triassic deposits of Hungary.

It is obvious that Prospondylus, as employed by Frech and Licharew, is synonymous in all respects with Pseudomonotis. The resilifers in American species range from symmetrical to very oblique. Licharew, like many other writers, has stressed the importance of shell thickness for distinguishing species and genera. I suspect that many of the Paleozoic pelecypods described as having very thin shells owe their apparent thinness to the fact that the inner orstracum is commonly absent, the aragonite having been dissolved away so as to leave only a thin shell layer of the more resistant calcite outer ostracum.

The general confusion surrounding Pseudomonotis has not been lessened by introduction of the term Aviculomonotis (Grabau, 1931, p. 325) proposal of which was incidental to description of the type species, A. mongoliensis Grabau, from the Permian of Mongolia. Aviculomonotis was founded without diagnosis in the following terms:

The reference of our species to the genus Pseudomonotis is questionable; probably it and the British form (Aviculopecten interstitialis Phillips), as well as the two following species, should both be referred at least to a distinct subgenus, for which the name Aviculomonotis Grabau (subgen. nov.) is here proposed with A. mongoliensis as the genotype.

An examination of the figures of A. mongoliensis reveals no characters by which the species might be distinguished from a typical Pseudomonotis s. s., nor does Grabau state in the description how he would distinguish Aviculomonotis from typical Pseudomonotis. I cannot agree that Aviculopecten interstitialis (Phillips), a typical representative of Aviculopecten. from the British Lower Carboniferous rocks, is closely related to Aviculomonotis mongoliensis Grabau. Until satisfactory means for distinguishing Aviculomonotis from Pseudomonotis are made known, it seems best to place Aviculomonotis in the synonymy of Pseudomonotis s. s.

Geologic range—A few decades ago Pseudomonotis was regarded as an index to Permian or later rocks. This supposition resulted from the fact that Pseudomonotis is not found below the Permian in western Europe where the genus was first made known. The fact that marine Upper Carboniferous rocks are mostly lacking in this region, however, makes this observation of the lower limit of geologic range of little significance.

Typical Pseudomonotis appears in America in the Morrow subseries of the Pennsylvanian rocks (Upper Carboniferous) in Arkansas. This occurrence, represented by precursor Mather, inflata Mather, and P. aurisculpta Mather, is apparently the earliest recorded appearance of the genus. It is possible that the habit of fixation had not been acquired in this tribe before Pennsylvanian time, in which case the Mississippian ancestors of Pseudomonotis would very likely have more nearly the characteristic pectinid form than the later species. A specimen of Pseudomonotis sayrei, n. sp., shows the curious feature of a smooth left valve and a costate right valve at a juvenile stage preceding fixation. P. hawni and some other species of Pseudomonotis became attached so early in life that right valves do not exhibit any recognizable prefixation stage. If Pseudomonotis, as defined here, is monophyletic we must look for an ancestor having a smooth left valve of marked convexity and a nearly flat costate right valve, in which the costae increase in number by intercalation. There should be no marginal sinus below the posterior auricles. The outer ostracum of the right valve should be irregularly prismatic, as in Pseudomonotis, and the hinge characters should be like those of the Aviculopectinidae. Unfortunately, it is impossible at the present time to obtain this information from the literature on any Lower Carboniferous species.

The genus Pseudomonotis ranges completely through the Pennsylvanian series and Permian system. It is commonly recorded in the Mesozoic systems but many of these citations refer to the group of "Pseudomonotis" ochotica, which does not appear to me to be congeneric with the Paleozoic forms. It is highly probable that there are Triassic derivatives of Pseudomonotis, but to my knowledge such relationship has not yet been demonstrated.


Plate 17, figures 11a, b; Plate 18, figures 8-16

Monotis Hawni Meek and Hayden, 1858, Albany Inst., Trans., vol. 4, p. 76; 1859, Philadelphia Acad. Nat. Sci., Proc., p. 28.
Eumicrotis Hawni Meek and Hayden, 1864, Paleontology Upper Missouri, p. 54, pl. 2, figs. 5a-c.
Eumicrotis Hawni var. ovata Meek and Hayden, 1864, Paleontology Upper Missouri, p. 55, pl. 2, figs. 5a, b.

Large numbers of Pseudomonotis occur at several horizons in the Big Blue series of Kansas and Nebraska. Locally limestone beds in some cases shaly, are filled with representatives of the genus. I am identifying these Big Blue forms with P. hawni Meek and Hayden. In spite of the local abundance of this species, well-preserved specimens are exceedingly rare, for almost all of these fossils are preserved as impressions or subinternal molds. In few instances is the shell substance completely retained.

P. hawni shows clearly the distinctive characters of the genus, additional features of specific nature being its variable form, ranging in plan from circular to subovate; left valve only moderately convex in most individuals, and having an only moderately inflated umbo with a relatively sharp beak; a large proportion of specimens exhibit an ill-defined posterolateral sulcus extending radially from the umbo of the left valve, producing an obscure posterior lobation of the shell; ornamentation relatively coarse, consisting in average specimens having a height of 3 1/2 to 4 cm. of about 10 coarse scaly costae separated by 3, or rarely 5, finer, nearly smooth costae, of which the middle one is of intermediate size; the number of coarse, scaly costae is only relatively constant, because in individual lots I have observed occasional specimens having as few as 8 and as many as 14 of the coarse costae.

Figure 33Pseudomonotis hawni (Meek and Hayden). Upper figure, A-B, a juvenile left valve, showing narrow beak, convexity, form, and ornamentation, approximately X 7; lower figure, profile of a mature left valve, X 2, showing convexity from the beak (right) to the ventral margin (left); camera lucida drawings. [Image scaled and magnifications adjusted for web presentation.]

Pseudomonotis hawni (Meek and Hayden).

Remarks—Probably the most constant and characteristic feature of the species is the distinctive form and convexity of the beak, which permits a ready distinction of this form from the similar Pseudomonotis beedei, n. sp. The posterior auricle in juvenile P. hawni is relatively short and more reduced than in P. beedei, and the beak is very much more pointed and pronounced in typical specimens. The largest observed specimen of P. hawni has a length and height of about 50 mm. Most individuals have only an obscure left anterior auricle and byssal sinus, differing in this respect from the well-defined byssal sinus found in the older species.

The right, or lower valve is flat or slightly convex, and except for the beak area is ornamented like the left with intercalculating costae, which are, however, noticeably finer than those of the opposite valve. A cicatrix of attachment appears to be present invariably at the umbonal area; in several specimens this scar measures 1 to 2 1/2 cm. across. Radial ornamentation begins beyond the scar.

Comparison—Adult specimens of Pseudomonotis commonly exhibit such variability that considerable difficulty has been experienced by paleontologists in discriminating species. It has been my experience that this difficulty of identification decreases where abundant well-preserved material is at hand. One cannot satisfactorily identify poorly preserved, or isolated specimens of Pseudomonotis, but I have found that collections containing a few good specimens of P. hawni from the upper half of the Big Blue series can be distinguished readily from adequate collections of the similar, much older, P. beedei, n. sp. Greater difficulty is experienced in dealing with specimens from the lower part of the Big Blue series, because this material consists chiefiy of isolated or poorly preserved specimens. There appears to be considerable variation among these specimens, and I anticipate that it may ultimately be desirable to exclude some of them from P. hawni. The diagnosis given above concerns only the typical P. hawni from the Chase and Sumner groups. In addition to having a much more prominent and sharper beak on the left valve, P. hawni differs from P. beedei in being less gibbous and in having sparser and slightly coarser ornamentation.

Material—The holotype of P. hawni (U. S. Nat. Mus., No. 3,958) is an internal mold retaining the impressions of both valves. The external ornamentation is not shown, but some paratypes from the same locality exhibit the essential features of the ornamentation of the left valve. The matrix is a grayish-buff, dolomitic limestone filled with the molds of tiny fossils. The length of the specimen is 37 mm.; height, 36 mm.; hinge length, 20 mm. The types of P. hawni var. ovata (U. S. Nat. Mus., Nos. 1,157, 1,158) occur in dense dolomitic limestone, and are preserved in the form of molds. These types of ovata came from "near Cottonwood Creek," Kansas. Prof. M. K. Elias, who is familiar with the stratigraphy of this region, informs me that the horizon of abundant Pseudomonotis along Cottonwood creek is the Herington limestone. After an examination of the type specimens and specimens from the Herington limestone supplied me by Professor Elias, I am convinced that the original types came from this horizon.

In addition to the types of P. hawni and the variety ovata a large number of fine specimens from the Herington limestone, as well as several dozens of isolated specimens from various horizons, were used as the foundation for the foregoing description.

Almost invariably, specimens of P. hawni that have come under my observation occur in a matrix of silty argillaceous limestone, or cavernous dolomitic limestone. Commonly, the only remaining part of the shell in argillaceous limestone is the nuter ostracum of both valves. In dolomitic limestone, even this is generally gone, so that preservation is in the form of internal and external molds. At many horizons in the Big Blue series these shells are incrusted with a calcareous cover that resembles the alga, Somphospongia multiformis Beede. A number of shells show the effect of boring organisms and exhibit encrusting worn tubes, evidence of the inactive habits of the host. Generally .he shells of P. hawni occur in large numbers in fairly thin, persistent zones, and they are commonly associated with species of Aviculopecten, Bakewellia, and Myalina, among pelecypods, and Juresania of the brachiopods. P. hawni is a gregarious species and locally the shells of this form are overwhelmingly predominant in the faunules.

Occurrence—Lower Permian. P. hawni is especially characteristic of the upper part of the Big Blue series (Lower Permian), in the northern MidContinent region. Less typical forms identified with the species are common in the lower part of the Big Blue series, but are not found in older rocks. The holotype of P. hawni was collected from "near the mouth of Smoky Hill fork of Kansas river, Kansas." The entire Big Blue series is exposed in the vicinity of the mouth of the Smoky Hill, but it seems most likely from the appearance of the specimen that it came from one of the limestones in the Chase or Sumner groups, very probably the Herington limestone.

In the collections at hand the species has been identified in the Burr limestone, Florena shale, Middleburg limestone, Crouse limestone, Funston limestone, Wreford limestone, Krider limestone, and Herington limestone. Undoubtedly the species will be. discovered at other horizons in the Big Blue series.


Plate 18, figures 17, 18

Pseudomonotis sublaevis Girty, 1909, U. S. Geol. Survey, Bull. 389, p. 80, pl. 9, figs. 1,2 (not 3). Yeso formation, San Andreas, New Mexico.

Girty's description:

Shell large. Shape subovate, rather irregular. Hinge shorter than the width below, ears small.
Surface of the left valve with obsolescent sculpture. In the umbonal region it is marked by fine, irregular, more or less wavy costae, a few of which, arranged at rather regular intervals, are somewhat larger than the others. In the course of growth the smaller costae as a rule soon die out, while a few of the larger ones, from 1 to 12 or more in number, much increased in size, pass on to the ventral border. More rarely some of the smaller costae are persistent. The whole surface is also crossed by closely arranged, irregular, concentric, lamellose lines and wrinkles.
This species is related to P. hawni, but is distinguished by its obsolescent sculpture and by the rarity or absence of spinel ike scales springing from the larger costae. These could hardly fail to be preserved upon our specimens if originally present, and they were apparently developed very rarely, perhaps not at all.

Comparison—After examination of the type specimens of this species I am inclined to agree with Doctor Girty that this form is probably distinct from P. hawni, but the shell preservation is rather poor and it is possible that the radial ornamentation may be more pronounced in perfectly preserved specimens.

Material—My observations were made on the three specimens figured by Girty in the original description of the species. His figure 3 is probably a Pseudomonotis hawni, and appears to belong to a different species from the other two. Figured types, U. S. Geol. Survey, Nos. 1,420 (holotype), 1,421, 1,422.

Occurrence—Permian, Yeso formation, San Andreas Mountains, New Mexico, east of Engle, in red beds about 700 feet above the top of a massive red sandstone.


Plate 16, figures 2, 3

Pseudomonotis cf. hawni Beede, 1899, Kansas Univ. Quart., vol. 8, p. 83, pl. 19, figs. 7a-f.
Pseudomonotis hawni (part) Beede, 1900, Kansas Univ. Geol. Survey, vol. 6, p. 132, pl. 15, figs. 1a-d.
Pseudomonotis hawni Sayre, 1930, Kansas Geol. Survey, Bull. 17, p. 112, pl. 9, figs. 1, 2.

As early as 1899, Beede recognized the characters by which this form may be distinguished from the similar P. hawni, but he did not venture at that time, or subsequently, to propose a distinct name for the form under consideration. This is probably one of the most variable species of Pseudomonotis. In spite of this general lack of uniformity in adults, the characters of the juvenile shell, as recorded in the beak of the left valve, are surprisingly constant and are very distinctive. The end of the beak in P. beedei is relatively flattened, scarcely any more convex than the general surface of the umbo, and is rather poorly defined in most specimens. In this respect the species resembles P. equistriata Beede and P. robusta Beede, with which it is associated. The hinge is relatively long at the juvenile stage, so that the shell outline is subrhombic, with a distinct prosocline obliquity. In P. hawni, on the other hand, the beak is well defined even in juveniles, and the hinge is distinctly shorter than the body of the shell.

The more obvious but less constant distinguishing features of P. beedei are the marked convexity of the left valve and inflation of the umbo. Commonly the whole valve is arcuate, with a strongly in curved beak.

Figure 34Pseudomonotis beedei Newell. Upper figure, A-B, successive growth stages on the beak of a characteristic left valve, approximately X 7, showing the rhombic form, relatively flattened beak, and radial ornamentation; the constriction around the beak shown in A is an accident of growth. Lower figure, profile of the holotype, a left valve, beak at the right, ventral margin at left, X 2. Camera lucida drawings. [Image scaled and magnifications adjusted for web presentation.]

Pseudomonotis beedei Newell.

The ornamentation is generally, but not invariably, finer and more dense than in P. hawni, resulting in a greater number of costae in the former species. The number and coarseness of costae in P. beedei is highly variable. In general, there are two types of costae-coarse scaly or spinose costae, and fine costae, 3 to 7 or more of which are implanted between the coarse costae. The fine costae of a few specimens are also scaly, and there is a general tendency for imbricating scaly spines to be produced on all costae near the shell margin of mature specimens. The number of coarse scaly costae observed in various specimens ranges from about 12 to 21, but these figures probably do not represent the extreme range of variation.

Most specimens display a more or less welldefined sulcus extending from the umbonal region toward the posteroventral margin of the left valve, producing a sort of posterior lobation of the shell. This feature, however, is obscure or lacking in some specimens. The largest measured specimen has a height of 50 mm. and a length of about 45 mm.

Comparison—Of the described American species of Pseudomonotis, P. hawni is most nearly like P. beedei. The latter differs from the former in the greater convexity shown by typical specimens, less prominent umbo and flattened beak of the left valve, more numerous costae, and greater variability in form.

Material—The species is founded on several scores of fairly well-preserved specimens, most of which were obtained from the Westerville oolite in the Kansas City region. The holotype (Kansas Univ., Paleont. Type Coll., No. 385) was obtained from the Haskell limestone near Lawrence, Kan.

This species has been found in three kinds of sediments. The most common occurrence is in oolitic limestone, three fourths of my material having been found in such rock, representing several horizons. Sandstone and argillaceous limestone have yielded a few individuals. The known occurrences of P. beedei were all associated with other kinds of mollusks, chiefly pelecypods and gastropods.

Occurrence—Upper Carboniferous, Drum oolite (Kansas City group) near Independence, Kan., has yielded a number of specimens of the species, most of which are preserved as internal molds. The Westerville oolite (Kansas City group), at Kansas City, is the most prolific source of specimens, and has furnished several scores of paratypes. Other horizons represented in my collections are: Springhill limestone (Lansing group), Captain Creek limestone (Lansing group), Haskell limestone (Douglas group) (holotype), Kereford limestone (Shawnee group), and Graham formation (Lower Cisco group, Texas) .


Plate 17, figures 3-7, 9, 10, 12-14

Pseudomonotis hawni equistriata Beede, 1899, Kansas Univ. Quart., vol. 8, p. 82, pl. 18, figs. 3-3b.
Pseudomonotis tenuistriata Beede, 1899, Kansas Univ. Quart., vol. 8, p. 81, pl. 18, figs. 1-ld (homonym of P. tenuisiriata: Bittner, 1899, supposed to have a few weeks priority).
Pseudomonotis kansasensis Beede, 1900, Kansas Univ. Geol. Survey, vol. 6, p. 133, pl. 14, figs. 1-1d (proposed as a new name for the preoccupied P. tenuistriata Beede). ——, Girty, 1903, U. S. Geol. Survey, Prof. Paper 16, p. 428, pl. 8, fig. 4; Girty, 1915, U. S. Geol. Survey, Bull. 544, p. 129, pl. 17, figs. 4, 4a. ——, Sayre, 1930, Kansas Geol. Survey, Bull. 17, p. 113, pl. 10, figs. 6, 7.
Pseudomonotis equistriata Girty, 1903, U. S. Geol. Survey, Prof. Paper 16, p. 428, pl. 8, fig. 5. ——, Sayre, 1.930, Kansas Geol. Survey, nun. 17, p. 114, pl. 9, figs. 10-12.

This form, because of variability in shape that exceeds even that of P. beedei, is one of the most perplexing of all American species of Pseudomonotis. The variability occurs even in relatively undistorted specimens and it affects the convexity of juvenile parts of the shell, although the form of growth lines in this part of the shell is fairly constant. I find it difficult to believe that the habit of attachment alone is responsible for the irregularity of this species. It also appears unlikely that the problem can be simplified by discriminatior of a larger number of separate species. Most, but not all, of my material comes from the Westerville oolite in the Kansas City region. In these collections the variation is so extreme and gradation so complete that I am disposed to bring together two of Beede's species P. equistriata and P. kansasensis under one name, P. equistriata.

The maximum size of mature growth varies, attaining a height and breadth in my largest specimen of about 60 mm. Some specimens, because of their extreme convexity and contortion, appear to have ceased their growth at a height of 20 mm. The larger specimens are relatively flattened and expanding.

Figure 35—A topotype specimen of Pseudomonotis equistriata Beede; ontogenetic changes on the umbo of a well-preserved, unworn left valve, and profile, showing the convexity, X6 (camera lucida drawings). [Image scaled and magnifications adjusted for web presentation.]

A topotype specimen of Pseudomonotis equistriata Beede.

The form of the juvenile parts of the shell is about the same as that in P. beedei. The single feature by which I have distinguished this variable form most definitely from others is the nature of the ornamentation. The body of the shell is covered by a very large number of fine, low, generally equal costae. The costae are not noticeably modified by scaly spines or projections, but are relatively smooth and regular. The species is not constant, however, even in character of ornamentation, because about half of my specimens show two or three orders of costae, one order being distinctly coarser than the other two. Even in these specimens the coarser costae are relatively fine and almost smooth.

At a shell height of about 25 mm. in several specimens, the costae range in number from about 100 to 125. The addition of new costae by implantation is very much more regular than is ordinarily the case in Pseudomonotis, so that in those specimens exhibiting two or three distinct sizes of costae, adjoining pairs of first order costae are generally separated by the same number of finer costae as other pairs.

Comparison—This species is more nearly like P. robusta than any other form known to me, differing from that species principally in the form and convexity of the juvenile portions of the left valve, as exhibited at the umbo. The umbo in P. robusta is remarkably flat and the hinge is relatively long in the juvenile stage as compared with P. equistriata. There are occasional specimens of P. beedei, n. sp., that could easily be confused with this one. P. beedei typically has a few relatively coarse, invariably scaly costae at maturity, separated by finer smooth costae.

Material—The material before me includes the holotype and several paratypes of P. equistriata and P. kansasensis, as well as scores of topotype specimens from the Westerville oolite at Turner, Kan., and Kansas City, Mo. The specimens are generally well preserved, but many of them are covered by a hard incrusting algal deposit that makes detailed study of the ornamentation difficult. Holotype of P. equistriata, Kansas Univ., Paleont. Type Coll., No. 389.1; holotype of P. kansasensis, Kansas Univ., Paleont. Type Coll., No. 370.1.

Specimens have been found mainly in oolitic and argillaceous limestones. The valves of P. equistriata are invariably separated in the oolitic occurrences, and other evidences of current action, such as crossbedding, indicate that the shells have been transported more or less, perhaps from another environment.

Occurrence—Upper Carboniferous. This species appears to be long ranging, for I have referred to it specimens from various parts of the Pennsylvanian series. By far the greater part of my material comes from the Westerville oolitic limestone in the Kansas City region, and it is possible that if large collections of the form could be obtained at other horizons some useful basis for further subdivision could be discovered. The species has been identified from the following formations: in Oklahoma, Wewoka; in Kansas, Missouri or Nebraska, Winterset, Drum, Westerville, Stoner, Kereford, Lecompton, Auburn, Florence; in Colorado, Rico; in Texas, Cisco (near Graham).


Plate 17, figures 1a-2

Pseudomonotis? robusta Beede, 1899, Kansas Univ. Quart., vol. 8, p. 82, pl. 18, figs. 2, 2a (not 2b, 2c); 1900, Kansas Univ. Geol. Survey, vol. 6, p. 133, pl. 14, figs. 2, 2a (not 2b, 2c).

This is a relatively rare species, but there are five specimens in the collections at hand, all of which exhibit the diagnostic features. P. robusta is ornamented like P. equistriata, having a large number of fine, subequal costae, none of which is spinose or markedly roughened by imbricating layers of growth. The holotype, which is by far the largest known specimen, has about 180 costae at the margin. This individual has a height of 42 mm. and a width of 48 mm. If the shell were flattened out somewhat, it would have a height of 60 mm. The length of the hinge is 22 mm.

It appears to me that the critical character of the species is not the dorsoventral arching of the shell as illustrated by the holotype, and stressed by Beede, but rather the distinctive shape and convexity of the juvenile part of the left valve. The primitive rhombic prosocline form, illustrated in the earlier juvenile stage of all species of Pseudomonotis, is retained to a height of 15 or 20 mm., and the hinge is relatively long, lending an archaic aspect to the shell. The relatively great hinge length is retained in at least some adults, although cementation obviously could produce distortion of the hinge in some shells. One juvenile specimen has a height of 17 mm., length, 14 mm., and hinge length of about 13 mm. At this size the shell is nearly flat. The beak is small, obscure, and only very slightly more convex than the surrounding area of the umbo. The right valve is unknown.

Figure 36—Camera lucida drawings of the umbonal area of a topotype, a left valve, of Pseudomonotis robusta Beede, approximately X 7. [Image scaled and magnifications adjusted for web presentation.]

Camera lucida drawings of the umbonal area of a topotype, a left valve, of Pseudomonotis robusta Beede.

Comparison—The character of the ornamentation of this species appears to ally it with P. equistriata, from which it differs in the form and convexity of the juvenile stages. There is no other species that has come to my attention with which it might logically be confused.

Material—The material at hand includes the holotype (Kansas Univ., Paleont. Type Coll., No. 388), two or three topotypes from the Westerville limestone near Kansas City, and in addition a specimen from the Winterset limestone. The WesterviUe specimens are all preserved in a matrix of oolite, whereas the Winterset specimen is associated with other mollusks in dark-gray, carbonaceous limestone.

Occurrence—Upper Carboniferous, recognized thus far only in the Westerville (Kansas City group) (holotype) and Winterset (Bronson group) limestones, associated with other mollusks.


In the middle Pennsylvanian (Missourian) rocks of Kansas, and lower and middle Upper Carboniferous (C2, C3) of the Donetz Basin in Russia, there occurs a suite of Pseudomonotis species that differ somewhat from typical Pseudomonotis. These forms, including P. spinosa Sayre, P. fredoniensis, n. sp., P. sayrei, n. sp., and P. mutabilis Fedotov, form a closely related group of such distinctive character that I was at first disposed to erect a new genus or subgenus for it. This first impression was abandoned, however, when I sought to draw up a diagnosis by which these forms could be set apart from Pseudomonotis.

In the American species, and probably also in the Russian P. mutabilis, there are two distinct growth stages. The umbo of the left valve is sharply set off from the later part of the valve in being nearly smooth, and markedly more convex. Distinct ornamentation is acquired just beyond the margin of this part of the shell. The distinctive nuclear or juvenile part of the shell is rather uniform in size and shape, ranging in height from about 4 to 9 mm. in various specimens of the three American species. The most striking feature of the nuclear shell, however, is a marked opisthocline obliquity and a height distinctly greater than the length. I suspect that the two well defined. growth stages—juvenile and adult—are correlated with the habits of the living animal. The juvenile portion of the shell is undistorted and uniform in quite a number of specimens, whereas the mature part of the shell is invariably irregular and contorted. The inference may be drawn from these observations that the habit of fixation was acquired when the shell had a height of 4 to 9 mm. This theory is substantiated by the fact that one of the specimens of P. sayrei retains both valves, and the nuclear stage of the right valve, unlike that of the left, is ornamented with distinct, unmodified fine costae, which are lost on the mature, presumably attached, part of the shell.

Judging from ontogeny, the ancestor of this group of Pseudomonotis was an opisthocline, or possibly acline, pectiniform shell with a smooth left valve and a costate right. valve. A group of Russian species P. gapeevi, P. jakovlevi, P. kumpani, and P. stepanovi, recently described by Fedotov (1932), possess characters that appear to place them in the ancestry of this distinctive group of P. spinosa. They differ in form, however, from juvenile P. spinosa in being more nearly acline, and having an acute instead of obtuse rear auricle. They are too symmetrical to be attached forms, and they should probably be established in a new genus.


Plate 18, figures 1a-2

Pseudomonotis spinosa (part) Sayre, 1930, Kansas Geol. Survey, Bull. 17, p. 114, pl. 10, figs. 3, 3a (not figs. 4, 4a).

The shell is relatively small for a Pseudomonotis, having a height and length of 25 mm. in the largest specimens at hand, with a hinge length of one third to one half of the length of the shell body. The beak of the left valve is very prominent and narrow, and somewhat in curved at the hinge. The umbo of the left valve is smooth and strongly inflated, changing markedly beyond a height of about 8 mm. At this size there is an abrupt decrease in convexity, and a curious ornamentation, consisting of numerous very fine, obscure costae intersected by closely spaced scaly growth varices, makes appearance. The intersecting radial and concentric lines produces a quincunxial arrangement of fine, depressed, scale-like projections. Beyond a shell height of about 17 mm. this striking ornamentation is modified by addition of 17 to 19 coarse plications which apparently have no relation to the fine costae. Right valve unknown.

Figure 37—Holotype of Pseudomonotis spinosa Sayre; A, rear view, beak at top, ventral edge below, X 6.4; B, plan view of the smooth nuclear part of the umbo, X 6.5; C, fear view, X 2, of the whole valve, showing three chief ontogenetic stages, differing in ornamentation; (camera lucida drawings). [Image scaled and magnifications adjusted for web presentation.]

Holotype of Pseudomonotis spinosa Sayre.

Comparison—Although there are only two specimens of this form in my collection, they are remarkably alike in all respects so that I do not doubt that this is a distinct species, although very closely related to P. sayrei, n. sp. From the latter species it differs chiefiy in the late appearance of the plications, because in P. sayrei the folding extends to the margin of the nuclear part of the shell.

Material—The above description is based on the lectotype (Kansas Univ., Paleont. Type Coll., No. 391.1) and a single paratype. I have separated a number of the original paratypes under the new name P. sayrei.

Occurrence—Upper Carboniferous, known thus far only in the oolite part of the Westerville limestone (Kansas City group) in the Kansas City region, Pennsylvanian.


Plate 18, figures 3, 5a, b

Pseudomonotis spinosa (part) Sayre, 1930, Kansas Geol. Survey, Bull. 17, p. 114, pl. 10, figs. 4, 4a (not figs. 3, 3a).

This species appears to be more variable than the closely related P. spinosa, but this may be only apparent because I have a better representation of P. sayrei than of P. spinosa.

Figure 38—Holotype of Pseudomonotis sayrei Newell; A, B, rear and side views respectively of the constricted area, showing the juvenile characters of convexity, form, and ornamentation of the nuclear part of the left valve, approximately X 7; C, an earlier stage, X 13.5, showing the abrupt change from the prosocline to acline obliquity; D, rear view of the entire left valve, X 2, showing the constricted umbonal area (shown in A and B) and the mature, plicate part of the shell; (camera lucida drawings). [Image scaled and magnifications adjusted for web presentation.]

Holotype of Pseudomonotis sayrei Newell.

This species is closely similar to P. sayrei, as evidenced by the same curious nuclear juvenile stage. In the present form, however, faint costae appear in some cases on the outer margins of the nuclear shell, becoming progressively coarser toward the periphery of the mature shell until they become distinct folds or plications. Some specimens, like the holotype, show very fine, almost invisible costae between the plications, and the fine costae are covered with scaly shell projections arranged in an obscure quincunx. Other specimens show no trace of the fine costae or the scales and some of these specimens are remarkably like a plicated Platyceras shell. It is possible that the non-scaly forms should be set aside as a distinct species, but I prefer to consider them as members of one variable species. The number of plications observed ranges from 13 to 21 in a few specimens in which a count can be made. The largest specimen is 30 mm. high. One small right valve in the collection is distinctly concave, and except for growth varices is nearly smooth in the mature part up to a height of 9 mm., where plications first appear; a nuclear area, deeply concave, occurs around the beak; this area is covered with very fine but distinct costae, of which 14 appear simultaneously. At a shell height of 8 mm., in this right valve, there are 24 of the costae, increase being by somewhat irregular implantation. The costae extend a short distance beyond the nuclear depression, which is only 6 mm. across in the direction of the shell height.

Comparison—This species is quite similar to P. mutabilis Fedotov from the Donetz Basin in Russia—indeed, it is not easy to indicate a ready means by which the American forms can be distinguished from some of the specimens figured by Fedotov. In general, it appears that the radial plications of the Russian specimens are more numerous than in P. sayrei, but I cannot be certain because Fedotov makes no statement as to the number of plications in the Russian form. The Russian form is recorded from stages C2 and C3 of the Donetz Basin, from beds corresponding approximately to our Des Moines and Missouri series, and since P. sayrei has not yet been encountered outside of Missourian rocks, these two species occur in rocks of about the same age.

Material—The collections before me include 14 specimens, several of which are syntypes of P. spinosa Sayre. The holotype (Kansas Univ., Paleont, Type Coll., No. 392.1) is a well-preserved specimen from the Westerville oolite. Most of the specimens occur in oolitic limestone, but one specimen was found by Prof. M. K. Elias in dark, carbonaceous limestone that is not oolitic, although associated with layers of oolitic limestone.

Occurrence—Upper Carboniferous. The holotype and 12 paratypes were obtained from the Westerville oolite in the Kansas City region; one specimen was found in the Drum oolite near Independence, Kan., and a single specimen was discovered in the upper, molluscan part, of the Winterset limestone at Kansas City, Kan. All of these occurrences bel?ng in the Missouri subseries, Pennsylvanian senes.


Plate 18, figures 4, 6, 7

A curious fauna occurs in the Stanton limestone (Stoner member) at Fredonia, Kan. This fauna is unlike that of the same or other formations elsewhere in Kansas in that many of the species and a few genera of invertebrates are unlike those found elsewhere in the Kansas section. It appears probable that this fauna is an exotic one, incorporating elements from some basin that was not ordinarily in free communication with the Kansas area. One of these exotic species is a peculiar Pseudomonotis, somewhat similar to the striking P. spinosa Sayre and P. sayrei, n. sp. My collection contains about 15 specimens, all left valves, of which the largest has a height and length of 50 mm. As in the preceding two species, there is an opisthocline, unornamented juvenile part of the shell at the umbo. Ordinarily this part of the shell is markedly more convex than the mature shell, and has a height of 8 or 9 mm.

The species is especially characterized by peculiarities of the costae on the mature part of the shell. The costae are numerous, subequal, and relatively narrow, ranging from 65 to 90 at a shell height of 30 mm. They are not modified by scaly projections, but are remarkable for their abundance and for the presence of local swelling and pinching that produces a marked rugose effect. The costae are relatively high and narrow and commonly are quite irregular in their course across the shell. Increase in numbers of costae is effected by irregular implantation. Right valve unknown.

Comparison—No species known to me can be confused with this one. Although obviously closely akin to P. spinosa and P. sayrei, it can be distinguished readily by the larger number of subequal, narrow and prominent costae. The little collection at hand exhibits more contortion of form than is shown in the adults of the two mentioned species, but this difference is probably not distinctive.

Material—The collection at hand contains 15 specimens including the holotype (Kansas Univ., Paleont. Type Coll., No. 393.1), all from a single locality and horizon. The types were obtained from a peculiar, granular suboolitic limestone, associated with a mixed brachiopod and molluscan fauna.

Occurrence—Upper Carboniferous. Confined, so far as known, to the Stoner member of the Stanton limestone, found at a cement plant quarry in Fredonia, Kan. Lansing group, Missouri subseries, Pennsylvanian series.

Miscellaneous Species of PSEUDOMONOTIS


Plate 17, figure 15

Aviculopecten aurisculptus Mather, 1915, Denison Univ., Sci. Lab., Bull., p. 224, pl. 15, fig. 12. Hale formation, East Mountain, Fayetteville, Ark.

This curious species was founded on a single specimen, the characters of which are so striking that the species may be easily recognized. The left valve is subhemispherical, symmetrical, and not in the least contorted. The regularity in form suggests that this was not a cemented shell. The byssal sulcus and anterior auricle are covered with fine intercalate costae which become progressively fainter toward the ventral margin and toward the shell body. Except for the 18 or more anterior costae and distinct lines of growth, the shell is quite smooth. The distinctness of the growth lines proves conclusively that the absence of costae over the shell body is not due to abrasion. Although the posterior part of the shell is missing, its outline can be inferred from the growth lines of the umbonal area. The posterior auricle was apparently obtuse, as in Pseudomonotis. The marked convexity of the single known specimen, a left valve, suggests a much flatter right valve, like that of Pseudomonotis, rather than one of the subequivalve Streblochondriinae.

Comparison—This species appears to be unique in the curious obsolescent character of the ornamentation.

Material—The only known specimen of this species is the holotype, Univ. Chicago, Walker Mus., No. 16,050.

Occurrence—Upper Carboniferous. Hale formation, Morrow subseries, East Mountain, near Klyce Spring, Fayetteville, Ark., Pennsylvanian series.


Plate 17, figures 8a-c

Pseudomonotis precursor Mather, 1915, Denison Univ., Sci. Lab., Bull., p. 217, pl. 15, figs. 1, 1a. Brentwood limestone, northeast of Fayetteville, Ark.

In many respects this form is like Pseudomonotis? auriculpta (Mather), and it is probable that they are rather closely related. The shell is subhemispherical, with an evenly inflated left valve and a shallowly concave right valve. The surface of the left valve in the holotype is covered with about 90 very fine intercalate costae which do not extend to the beaks, but leave a smooth area 3 or 4 mm. high on the umbo. The right valve is similarly ornamented up to a height of about 12 mm. where, in the holotype, there appears to be a cicatrix of fixation. The marginal area of the valve is devoid of costae and exhibits only lines and wrinkles of growth. The holotype has a height and length of about 13 mm.

Comparison—This species is characterized by its regular form and convexity, and by the remarkably fine costae.

Material—The species was based on two specimens, one of which, the holotype (Univ. Chicago, Walker Mus., No. 16,059), has formed the basis of my remarks.

Occurrence—Pennsylvanian series (Upper Carboniferous). Brentwood limestone, Morrow subseries, northeast of Fayetteville, Ark.

Unrecognizable Species of PSEUDOMONOTIS


Plate 16, figures 4a-c

Pseudomonotis inflata Mather, 1915, Denison Univ., Sci. Bull., p. 218, pl. 15, figs. 15, 15a. Kessler limestone, East Mountain, near city water reservoir, Fayetteville, Ark.
This species is based upon an internal cast (mold) of a left valve from the Kessler limestone and differs markedly from the members of this genus described from the Coal Measures in its greater inflation and peculiar outline.Mather.

No species of Pseudomonotis known to me can be recognized solely from internal molds. Until topotypes of P. inflata showing the external ornamentation are described this species cannot be utilized.

Material—Holotype, Univ. Chicago, Walker Mus., No. 16,057. Found in oolitic limonite in which various shells are preserved as external and internal molds.

Occurrence—Pennsylvanian series (Upper Carboniferous) . Kessler limestone, Morrow subseries, East Mountain, near city water works, Fayetteville, Ark.


Plate 16, figures 1a, b

Eumicrotis hawni var. sinuata Meek and Worthen, 1866, Illinois Geol. Survey, vol. 2, p. 338, pl. 27, figs. 12-14. Upper Coal Measures, bridge of north branch of Saline River, Gallatin county, Illinois.

This variety is not well founded, for the holotype and most of the paratypes are internal molds which do not display diagnostic features of the beaks. Possibly authentic topotypes can be obtained in the future and the variety (or species) finally may be placed on a firm basis.

Material—Holotype, Univ. Ill., Geol. Mus., No. 10,914. Found in dark, dense limestone.

Occurrence—Pennsylvanian series (Upper Carboniferous) "Upper Coal Measures," bridge of north branch of Saline river, Gallatin county, Illinois.

Other Species

Three forms were described in 1858 by Swallow (St. Louis Acad. Sci. Trans., vol. 1) from the Lower Permian of Kansas under the names Monotis halli, M. speluncaria var. americana, and M. variabilis. These forms were never illustrated, the types are hopelessly lost, and there is no record of the exact locality or horizon from which they came. Except for the fact that these names have been introduced into the literature, they may be ignored as specific entities. There is no assurance that these forms belong to Pseudomonotis.

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Kansas Geological Survey, Geology
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