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Systematic Paleontology
The Earliest Pectinoids
It was set forth clearly by Jackson, in his monumental "Phylogeny of the Pelecypoda," that modern Pteriidae and Pectinidae pass through a series of growth stages in which the shell form in the two groups is identical. The early growth stages in the modern forms correspond, at least superficially, to the adult form of several Paleozoic genera. It was Jackson's belief that the genus Rhombopteria, from the Silurian of Bohemia, represents the ancestral radical which gave rise on one hand to the Pteriidae through such genera as Leptodesma, and on the other hand to the Pectinidae (Pectinacea) through forms like Pterinopecten and Aviculopecten. In general, the consecutive form stages of a modern Pecten are similar in outline to the adults respectively of Rhombopteria, Pterinopecten, Aviculopecten, and Pecten. This growth sequence is so characteristic of modern Pectinacea that its phylogenetic significance cannot be lightly passed over. The evidence of ontogeny suggests that a form resembling Rhombopteria in general shape gave rise to one having the shape of Pterinopecten, which in turn evolved respectively into an Aviculopecten-like shell and one having the shape of a true Pecten. This phylogeny needs to be examined more closely in light of the paleontological evidence.
In a broad way, there are two kinds of ligament structures in Paleozoic pectinoid shells, otherwise quite similar, separating an older from a younger Paleozoic group. In the older group the ligament area of the shell is structurally like that of modern Arcidae, although there is no necessary implication of close relationship with the areas, The Arca kind of ligament, described on previous pages, is very distinctive and there is a good basis for supposing these older Paleozoic pectinoids had such a ligament. The genera Lyriopecten Hall, Pseudaviculopecten Newell, n. gen., Posidonia Brown, Palaeopecten Williams, and Pterinopecten Hall, are alike in having the Arca type of ligament area. These genera characterize beds ranging from Silurian to Mississippian age, inclusive, but there are a few stragglers that extended into the Pennsylvanian. In the following pages I propose to classify these Mid-Paleozoic pectinoids as a separate family in the Pectinacea, called the Pterinopectinidae.
In the Mississippian faunas another kind of ligament, similar to that in the modern Pteriidae, began to supplant the pterinopectinid structure, and apparently completely replaced it before Permian time. This later Paleozoic group, diversified into several subfamilies, I propose to class as the Aviculopectinidae. Presumably the Aviculopectinidae were derived from the Pterinopectinidae, because the latter group is, in general, older than the Aviculopectinidae, and because there is nothing in the older faunas so nearly like the Aviculopectinidae as are the Pterinopectinidae. It is appropriate now to give a diagnosis of the family Pterinopectinidae, and some brief comments on genera of the family known to me. Further characteristics of the family can be defined in the future, when more has been learned about this group. In seeking an ancestral radical of the Pterinopectinidae, I should expect, on theoretical grounds, a form organized like the equivalve Ptychodesma Hall and Whitfield. This genus is probably dimyarian and lacks a distinct byssal notch, but there is a slight tendency toward an anterior lobation prophetic of such a notch. Of course Ptychodesma itself probably should not seriously be considered because it is supposed to be restricted to the Devonian, whereas Rhombopteria was described from the Silurian.
Figure 14—Hypothetical phylogeny of the family Pterinopectinidae; entirely tentative and subject to revision.
Family Pterinopectinidae Newell, n. fam.
Commonly prosocline, rarely acline, smooth or ornamented, more or less pectiniform shells in which the right valve is primitively the less convex of the two; ligament area similar to that in some Arcidae, i. e., without resilifers but bearing one or a series of asymmetrical chevron grooves below the beaks; posterior auricle longer than anterior, but commonly conspicuously less well differentiated.
Phylogeny
Presumably these earliest of all pectinoids originated in noncostate, prosocline, Early Silurian forms like Rhombopteria, probably structurally like the Devonian Ptychodesma. Neither Rhombopteria nor Ptychodesma are "pectinoid" in general physiognomy, but they agree well, at least in form, with the earliest growth stages of later Pterinopectinidae.
The exact derivation of the Silurian genus Palaeopecten and the Devonian genera Pterinopecten, Pseudaviculopecten, Lyriopecten and Vertumnia is not yet known to me. It is obvious that Vertumnia, with its resupinate convexity, and Lyriopecten, with the aborted anterior auricles, are both highly specialized genera, apparently leaving no descendants.
Half-grown individuals of Posidonia have the general form of Rhombopteria and suggest that Posidonia is a direct descendant of the Silurian genus.
Except for the bifurcate costae on the right valve Dunbarella Newell, n. gen., is very similar to Pterinopecten, indicating that Dunbarella is an immediate derivative from Pterinopecten. Stratigraphic evidence for this relationship should be sought in early representatives of Dunbarella papyraceus from the Carboniferous of western Europe.
Pterinopectinella is like Pseudaviculopecten except for a curious spinose ornamentation and bifurcate costae on the right valve. In view of the fact that Pterinopectinella is not now known in the Devonian, where Pseudaviculopecten reaches its acme of development, it seems probable that Pterinopectinella is a descendant of Pseudaviculopecten.
Genus PTERINOPECTEN Hall, 1883
Plate 2, figures 4a-c
Pterinopecten Hall, 1883, Paleontology of New York, vol. 5, part 1, Lamellibranchiata 1 (advance copy), p. 3.
Genolectotype Pterinopecten undosus (Hall), Middle Devonian, designated by S. A. Miller, 1889, North American Geology and Paleontology, p. 507.
Shell elongate, subquadrate, prosocline; hinge line shorter than shell length, met by the rear margin at an obtuse angle; umbonal folds low, obscure, diverging at 100 degrees or more; auricular sulci obscure, the left anterior being more pronounced than the others; in some specimens the umbonal folds are scarcely distinguishable; posterior auricular sinus obscure or lacking; both valves ornamented alike by fine intercalate costae and finer concentric fila, spaced about the same distance apart as the costae; ornamentation of auricles similar but slightly less prominent than that of the shell body; a well-defined cardinal costa on each valve; ligament area narrow, flat, with chevron grooves extending' the length of the area and having their apex below the beaks; one or two of the earliest formed grooves do not form complete chevrons in some instances, but extend only behind the beaks.
This diagnosis is drawn up from nine specimens of the genotype species, from the Hamilton group of western New York. Two or three specimens show traces of a thin lamellar shell layer that included at least the outer ostracum. However, further observations will have to be made before this shell structure can be described properly and evaluated.
Figure 15—Camera-lucida drawing of the juvenile stages of a left valve of Pterinopecten undosus (Hall), genotype of Pterinopecten, showing the rhombic form and protuberant beak.
Genus RHOMBOPTERIA Jackson, 1890
Rhombopteria Jackson, 1890, Phylogeny of the Pelecypoda, Boston Soc. Nat. Hist., Mem., vol. 4, p. 380.
Genotype, Avicula mira Barrande, Silurian.
Because Rhombopteria mira conforms quite well in shape with a very early growth stage in Pectinacea, it has been generally assumed that this particular genus is the ancestral form from which later Pectinacea and Pteriacea were derived. As far as I am aware, nothing is known of the ligament area or hinge structures in the genotype species. Weigelt (1922) and Kegel (1925) have discussed the genus at length, but their personal observations did not include the type species. Weigelt (1922, p. 59) has shown how similar Rhombopteria is externally to young specimens of Posidonia. He demonstrated a ligament area of the pterinopectinid type in Posidonia. If Rhombopteria is in reality closely related to Posidonia, it must have a similar hinge structure.
Genus PALAEOPECTEN Williams, 1913
Palaeopecten WILLIAMS, 1913, U. S. Nat. Mus. Proc., vol. 45, p. 331.
Genotype, Palaeopecten cobscooki Williams, Silurian.
Range, Silurian.
This curious genus clearly is distinct from all other Pterinopectinidae in possessing slender, but distinct auricular crura. Williams described this form as possessing a central resilifer, but after examining the type specimens of P. cobscooki at the U. S. National Museum I believe that the specimens, which are internal molds, are not sufficiently well preserved below the beaks to determine whether or not there was a central resilifer. The chevron grooves of the Pterinopectinidae are well shown and it seems improbable that both kinds of ligament were combined in Palaeopecten.
Genus POSIDONIA Bronn, 1828
Posidonia BRONN, 1828, Zeitsch. f. Min., vol. 1, p. 262.
Genotype, Posidonia becheri Bronn, Lower Carboniferous.
Range; Lower Carboniferous (Mississippian) to upper Carboniferous (Pennsylvanian, Des Moines subseries).
Weigelt (1922) has made an important contribution to the study of Posidonia and similar forms. He has shown that an early stage Posidonia becheri has an incipient byssal notch, and a shape like Rhombopteria. The ligament area is that of the Pterinopectinidae. Weigelt is inclined to give the genus Posidonia very wide limits and to suppress terms like Rhombopteria Jackson and Caneyella Girty as subjective synonyms. The adult Posidonia is not auriculate nor does it have a byssal notch. It would appear to be a side specialization from the main pterinopectinid stem. I doubt the propriety of placing Caneyella Girty, as represented by the costate genoholotype C. richardsoni Girty, with the noncostate and otherwise quite different Posidonia.
Of the various American Pennsylvanian posidonias that have come to my attention, only Posidonia fracta (Meek) is a valid species, all other names being synonyms or referring to other genera.
Three Pennsylvanian species were described by Lea (1853) and referred provisionally to Posidonia: Posidonia clathrata, Posidonia? distans, and Posidonia peretriaia. Girty (1908) has shown that the first of these is a costate pectinoid, but otherwise unidentifiable, the second is a gastropod, and the third possibly an Edmondia.
Posidonia moorei Gabb (1860) is probably an Astartella, and Posidonomya striata Stevens is probably the right valve of Aviculopecten. A cursory examination of the types of Posidonomya? recurva and Posidonomya pertenuis Beede (1899) from upper Pennsylvanian (Virgil) rocks shows that these species are not posidonias.
POSIDONIA FRACTA (Meek) Plate 3, figures 15-17
Posidonomya fracta Meek, 1875, Paleontology, Ohio, vol. 2, p. 333, pl. 19, figs. 7 a, b. Lower Mercer limestone (upper Pottsville), Flint Ridge, Ohio.
Posidonia girtyi Morningstar, 1922, Ohio Geol. Survey, Bull. 25, p. 214, pl. 12, figs. 1-4. Lower Mercer limestone (upper Pottsville), Rock Hollow, Vinton county, Ohio.
Posidonia vintonensis Morningstar, 1922, Ohio Geol. Survey, Bull. 25, p. 216, pl. 12, figs. 5, 6. Lower Mercer limestone (upper Pottsville), Rock Hollow, Elk township, Vinton county, Ohio.
Meek's description:
Shell obliquely subovate, compressed, very thin; posterior basal margin regularly rounded; posterior dorsal edge nscending obliquely forward to the hinder extremity of the hinge, which it meets a t an obtuse angle; anterior margin descending or truncated more or less nearly vertically from the beaks above, and rounding obliquely into the base below; hinge line straight, very short, and ranging at an angle of about 45° to 60° above the longer oblique axis of the valves; beaks terminal, very oblique, and projecting very little or not at all above the hinge margin; surface marked by regular concentric undulations, with intermediate parallel striae.
Length of a narrow right valve, 0.72 inch; breadth of same, 0.43 inch; length of hinge, 0.22 inch.
There is no doubt that Morningstar's material of Posidonia girtyi and P. vintonensis came from the same horizon as Meek's types of P. fracta, and being in all respects like the previously described fracta, I am placing the three names in synonymy. An examination of the growth lines of mature P. girtyi shows that the associated P. vintonensis represents merely a juvenile growth stage of the former species.
Material—Only Morningstar's types were examined, and under circumstances that precluded a detailed study.
Occurrence—Upper Carboniferous, in black carbonaceous, somewhat calcareous shale at top of the lower Mercer limestone (upper Pottsville), Vinton county, Ohio.
Genus LYRIOPECTEN Hall, 1877
Plate 2, figure 11
Lyriopecten Hall, 1877, in S. A. Miller, Am. Paleozoic Fossils, p. 13.
Genotype, by monotypy, Avicula orbiculata Hall, Middle Devonian.
Range, Devonian.
The genotype of Lyriopecten generally has been thought to be L. magnificus Hall, dating from S. A. Miller's designation in 1889 (p. 487). In 1877 Miller published a list of manuscript names of Hall's species under the manuscript genus Lyriopecten. Included in the list was a single previously published species Lyriopecten orbiculatus (Hall). Since all of the other species were nomina nuda the species orbiculatus automatically becomes the type. Frech (1891, p. 27) introduced the term Orbipecten for Hall's Lyriopecten on the grounds that Luriapecten is a homonym of the older Luropecten Conrad. His arguments are not correctly founded because the two terms are compounded from different stems: lyrion, and lyra.
Genus VERTUMNIA Hall, 1884
Vertumnia HALL, 1884, Palaeontology of New York. vol. 5, part 1, Lamellibranchiata I, p. xii.
Genolectotype, Vertumnia reversa (Hall), Middle Devonian, designated by Pohl, Devonian of Wisconsin, Lamellibranchiata I, Milwaukee, Public Mus., Bull., p. 59, 1929.
Range, Devonian.
The hinge structures of this genus are unknown, but the general expression is pterinopectinoid. Vertumnia is exceptional in having a flat or concave left valve and a convex right valve.
Genus PSEUDAVICULOPECTEN Newell, n. gen.
Plate 2, figures 1-3, 19, 20
Prosocline, costate, Pterinopectinidae, in which the subequal auricles are well differentiated from the shell body, both in form and ornamentation, umbonal folds and auricular sulci clearly defined; hinge margin shorter than the shell length; a broad and deep sinus present at the outer margin of each auricle; ornamentation similar on both valves, consisting of moderately fine intercalate costae crossed by finer fila.
Genotype—Aviculopecten princeps (Conrad), Middle Devonian.
Range, Devonian, Mississippian?
Remarks—It seems highly probable that many of the species classed by Hall (1884) as Aviculopecten belong here. The hinge characters of several of the Devonian species are not yet known. The Mississippian Aviculopecten amplus Meek and Worthen is a pterinopectinid and probably belongs here.
Genus DUNBARELLA Newell, n. gen.
Orbicular or subquadrate, prosocline Pterinopectinidae having costate ornamentation on both valves, intercalate on the left and bifurcate on the right, and with or without costae on the auricles; concentric fila absent or very subdued: distinct posterior umbonal fold lacking, anterior one obscure; anterior sulcus narrow and well defined, posterior one broad and obscure, or lacking, auricles subquadrate, except the anterior one of the right valve, which is rounded; outer ostracum of both valves prismatic with the prisms of irregular size and not regularly arranged in a pattern; inner ostracum unknown; right valve slightly flatter than the left, cardinal costae obscure or lacking. The name is given in honor of Dr. C. O. Dunbar, of Yale University.
Genotype—Aviculopecten whitei Meek, upper Pennsylvanian.
Range, Mississippian, Pennsylvanian.
Remarks—This group is obviously closely related to Pterinopecten and very likely is a direct descendent from the Devonian genus. The only conspicuous difference lies in the bifurcate costae of the right valve. The juvenile stages of Dunbarella are strikingly like that of Pterinopecten. The well-known Aviculopecten papyraceus (Sowerby) from the Coal Measures of western Europe is a member of this genus.
Three species of Dunbarella can thus far be profitably distinguished in the American Pennsylvanian rocks, although I am sure that several more species can eventually be discriminated. Dunbarella rectolaterarea characterizes the older Des Moines rocks and does not extend above the Des Moines subseries. Most of the occurrences appear to be in the Cherokee shale or equivalent horizons.
Dunbarella knighti, n. sp., is known thus far from the uppermost part of the Cherokee shale (Allegheny equivalent), above the Bevier coal horizon. This species is intermediate in character between Dunbarella rectalaterarea and D. whitei, of which the latter characterizes Virgil (upper Pennsylvanian) rocks.
Probably future discoveries will bring to light additional evidence that the species of Dunbarella can be arranged in simple, stratigraphically useful genetic series.
| Measurements in Species of Dunbarella Newell, n. gen. | |||||||
|---|---|---|---|---|---|---|---|
| Species | Specimen No. |
Length, mm |
Height, mm |
Hinge length, mm |
Umbonal angle, degrees |
Body costae |
Costae on front auricle |
| whitei | L 1a | 16 | 15 | 11 | 105 | 28 | |
| L 2 | 16 | 15 | 12 | 110 | 27 | ||
| L 3 | 16 | 16 | 12 | 95 | 31 | ||
| L 4 | 21 | 20 | 17 | 99 | 27 | ||
| R 5 | 22 | 21 | 19 | 110 | 24 | ||
| R 6 | 24 | 21 | 20 | 115 | 26 | ||
| R 7 | 16 | 14 | 13 | 106 | 32 | ||
| knighti | L 1b | 25 | 22 | 17 | 78 | 7± | |
| L 2 | 24 | 23 | 16 | 5 | |||
| R 3 | 24 | 22 | 17.5 | 3 | |||
| rectalaterarea | L 1 | 25 | 27 | 21 | 77± | 8+ | |
| L 2 | 22± | 23 | 18 | 6 | |||
| L 3 | 21± | 22 | 16 | 78± | 5 | ||
| L 4 | 22 | 23 | 18 | 83 | 7 | ||
| a. Lectotype. b. Holotype. L. Left valves. R. Right valves. |
|||||||
DUNBARELLA WHITEI (Meek)
Plate 1, figures 9-11; Plate 2, figures 12-18
Aviculopecten whitei Meek, 1872, U. S. Geol. Survey, Nebraska, Final Rept., p. 195, pl. 4, figs. 11 a-c.
Shell orbicular, prosocline, flattened; hinge slightly shorter than the shell length; posterior auricle twice as long as anterior, flat, and smooth, generally not set off from the shell body by a fold, or by more than an almost indistinguishable broad sulcus; anterior fold absent, but the small triangular auricle is distinctly set off by a shallow, narrow sulcus; costae lacking on both auricles; body of left valve ornamented by a few low, rather closely spaced, intercalate costae arranged in commonly two, rarely three ranks; right valve with similar costae that increase by bifurcation, the first splitting taking place at a shell height of 4 to 7 mm, commonly about 5 mm; outer ostracum in both valves composed of polygonal prisms of irregular shape and size, averaging about 25 to 30 microns in diameter in adult shell. The rear shell margin meets the cardinal margin at about 120 degrees. A single one of my specimens shows traces of the chevron grooves of the pterinopectinid hinge.
Figure 16—American species of the new genus Dunbarella. Evolution in the genus appears to be expressed in (1) increasing posterodorsal angle of the rear auricle, (2) reduction and loss of costae on the rear auricle, and (3) forward migration of the beaks.
Measurements for specimens of Dunbarella whitei are given in the table [previous].
Comparison—This species can be distinguished readily by the noncostate auricles and relatively broad flattened costae on the shell body.
Material—This description was based on the original types studied at the U. S. Nat. Mus., No. 6,983, and some other characteristic specimens (Yale Univ., Peabody Mus., No. 14,462) from beds of nearly the same age as those from which the types were collected. These specimens in every case retain only the outer prismatic ostracum, the inner part having been dissolved away. Although the external ornamentation is very subdued, it is reflected rather well on molds of the inner surface of the prismatic layer.
Occurrence—Upper Carboniferous. The types were collected by Meek from fine argillaceous gray shale near the level of the boat landing at Nebraska City, Neb. This is near the level of the Willard shale (Wabaunsee). Other specimens in our collections came from the Pierson Point shale, one mile south of Falls City, Neb., Severy shale, Church farm, a short distance east of Du Bois, Neb. Virgil subseries.
DUNBARELLA KNIGHTI Newell, n. sp.
Plate 2, figures 8-10
This species is very much like D. whitei (Meek) in size and shape, but is distinguished by the occurrence of costae on both auricles and by a sub central location of the beaks along the hinge. The costae uniformly are smaller and less distinct toward the hinge so that the rear auricle in each valve is not sharply defined by differences in ornamentation. Since the rear auricles are so poorly defined, it is not possible to measure the umbonal angle. Whereas there are rarely over 30 costae on either valve in D. whitei, there are generally between 70 and 90 on each valve of D. knighti. The angle between the cardinal margin and the posterior margin of the shell is uniformly about 120 degrees. The outer prismatic ostracum is like that of D. whitei.
The name is given in honor of Dr. J. Brookes Knight who collected and donated the type material.
Measurements of specimens of Dunbarella knighti are given in the table [previous].
Comparison—In the characters of ornamentation Dunbarella knighti resembles D. rectalaterarea (Cox). From that species, however, it is easily distinguished by its orbicular shape and obtuse posterodorsal angle. The costate auricles and the nearly median position of the beaks distinguish this species from D. whitei.
Material—The types, Kansas Univ. Paleont. Type Coll., No. 237, about 20 in number, were presented to me by Dr. J. Brookes Knight as part of a very fine collection of pelecypods from the Pennsylvanian beds of the St. Louis outlier. The specimens are chiefly molds of the inner surface of the prismatic ostracum (subinternal), the inner ostracum with hinge and musculature having been dissolved.
Occurrence—Upper Carboniferous. The holotype and several topoparatypes were collected from fine bluish-gray argillaceous shale, and black, platy, carbonaceous shale of the Cherokee shale, at the Prospect Hill shale pit of the Missouri Portland Cement Company, Riverview Drive, St. Louis Mo. (Knight's locality 8, cycle A, member 8, lower part). Several paratypes, all in black shale are from the Cherokee shale, Abingdon, Ill. Des Moines subseries.
DUNBARELLA RECTALATERAREA (Cox)
Plate 2, figures 5-7
Avicula rectalaterarea Cox, 1857, Kentucky Geol. Survey, Paleont. Rept., vol. 3, p. 571, pl. 9. fig. 2.
Subquadrate dunbarellas, higher than long, with numerous crowded costae on auricles and shell body; ornamentation of auricles not well differentiated from that of shell body; posterodorsal angle abrupt, only slightly more than a right angle (less than no degrees); commonly there is an obscure sinus just below the posterior termination of the hinge so that the tip of the rear auricle is truly quadrate. A single specimen in my collection shows an imprint of the chevron grooves characteristic of the pterinopectinid hinge.
Measurements of specimens of Dunbarella rectalaterarea are given in the table [previous].
Apparently the original types of this species are lost. It is such a distinctive form, however, that I have but little doubt that my specimens are conspecific with or very closely related to those described by Cox.
Comparison—The relatively great height and quadrate form of this species serve to distinguish it from other known American dunbarellas.
Material&mgash;The above description was drawn up chiefly from a collection from Oakland City, Ind. (Yale Univ., Peabody Mus., No. 14,463). In addition there are three or four other collections of material, undoubtedly conspecific with the Indiana specimens, so that in spite of the rather fragmentary condition characteristic of specimens of the genus, the limits of variability are fairly well known.
Occurrence—Upper Carboniferous. Cox's types were said to have come from the black roof shale of No. 9 coal at the Kentucky Coal and Curlew mines, Union county, Kentucky. This horizon is in the Des Moines subseries, thought to be equivalent to the hard black shale under the upper Fort Scott limestone. In the collections at hand the species was found at Oakland City, Ind., 8 feet above the 4-foot coal at that place, probably in the roof of the Petersburg coal which is the same age as the preceding; "Coal Measures." Henry county, Missouri; Des Moines beds, Vermillion county, Indiana; Des Moines beds, Schuyler county, Illinois; probably just below the upper Fort Scott limestone. There are three specimens from the coal shaft at Leavenworth, Kan., probably from the Cherokee shale.
Genus PTERINOPECTINELLA Newell, n. gen.
Pterinopecten (in part) of authors.
Prosocline subquadrangular Pterinopectinidae having broad, poorly defined posterior auricles and well-defined small, anterior auricles; a small marginal sinus occurs just under the acute posterodorsal angle; ornamentation characterized by rather coarse spinose costae which increase by implantation in the left valve and by fission in the right valve; costae of the auricles slightly finer but otherwise undifferentiated from the body costae; spines relatively short, cylindrical, inclined toward the ventral surface at almost 45 degrees to the shell surface; left valve inflated, right valve nearly flat; fila absent or inconspicuous.
Genotype—Pterinopectinella welleri Newell, n. sp., middle and upper Pennsylvanian.
Range of genus, Mississippian to upper Pennsylvanian inclusive.
The so-called Pterinopecten granosus (Sowerby) and Pterinopecten eximius (Koninck) from the Lower Carboniferous of western Europe are characteristic species of Pterinopectinella, as is the Pterinopecten spinosus Fedotov from the Lower Carboniferous of the Donetz Basin in Russia (D4 limestone of series C4). In the Pennsylvanian the genus is as yet known only in the Missouri and lower Virgil subseries of the Mid-Continent region, and as far as I know this is its highest occurrence.
PTERINOPECTINELLA WELLERI Newell, n. sp.
Plate 3, figures 14, 18-24
Adult shell prosocline, about as long as high, subquadrangular; hinge nearly but not quite as long as the greatest length of the shell; beaks distinctly anterior to a mid-point on the hinge line, that of the left valve broad and gibbous in accordance with a subhemispherical form of the valve; right valve nearly flat except for a moderate convexity of the umbo; distinct umbonal folds lacking; anterior sulcus rather deep and moderately narrow, being depressed slightly below the general surface of the auricle; posterior sulcus very broad and poorly defined, about coextensive with the auricle; both valves ornamented on body and auricles with numerous spinose costae in three ranks, becoming uniformly a little less coarse on the posterior auricles; anterior sulcus without costae; concentric ornamentation obscure or lacking; spines relatively short, cylindrical, probably originally hollow, containing in the fossil state a large central core of calcite; in ontogenetic development spines appear nearly as early as the first appearance of the first order costae, occurring chiefly on the first and second order costae.
The name is given in honor of Dr. J. Marvin Weller of the Illinois Geological Survey.
Comparison—It would be difficult to distinguish this species from several of the Mississippian forms solely on the basis of the published illustrations and descriptions. The limits of variability within the genus appear to be rather slight. It is highly probable that other species in the Pennsylvanian can be discriminated when further material is discovered.
Material—Description of the species is based on eight specimens, six left valves, and two right valves, showing quite well the characters of ornamentation. The holotype, an internal mold, shows satisfactorily the ligament area. Holotype and two topoparatypes, Kansas Univ. Paleont. Type Coll., No. 358; paratypes, Kansas Univ. Paleont. Type Coll., Nos. 356 and 357; paratype, U. S. Nat. Mus., No. 27,88l.
Occurrence—Upper Carboniferous. The holotype and some topoparatypes were found in the uppermost sandy layers of the Stanton limestone (South Bend limestone member) at a cement plant, Fredonia, Kan. Two paratypes came from the Argentine limestone, Kansas City, Mo., and one from the oolitic Westerville limestone at Kansas City, Mo. Other specimens, too fragmentary for a positive identification, came from the Palo Pinto limestone, 3 miles west of Strawn, Tex.; Kansas City, Mo., exact horizon unknown; Farley limestone, Bonner Springs, Kan. All of these horizons are in the Missouri subseries. Several other paratypes were found in the Plattsmouth member of the Oread limestone (Shawnee group), Virgil subseries at Melvern, Kan.
| Measurements of Pterinopectinella welleri Newell, n. sp. | |||||||
|---|---|---|---|---|---|---|---|
| Specimen No. | Length, mm | Height, mm | Hinge length, mm |
Convexity, mm |
Chevron grooves, No. |
Costae on anterior auricle |
Total costae |
| L 1 | 43 | 41 | 10 | 5 | 3 | 43 | |
| L 2 | 32 | 32 | 30 | 7 | 4± | 2+ | 40± |
| L. Left valve | |||||||
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