Bef SRP eh ET PARE 0 ehh BLE OL P| eT th ae eet oF “Ft he rege Sore eee Nanak at se orheS oe ~ - rete = ee ee Postila PEABODY MUSEUM OF NATURAL HISTORY YALE UNIVERSITY NEW HAVEN, CONNECTICUT, U.S.A. Number 110 September 14, 1967 REVISION OF SYNCYCLONEMA (UPPER CRETACEOUS) AND COMPARISON WITH OTHER SMALL PECTINID BIVALVES AND ENTOLIUM IAN G. SPEDEN NEW ZEALAND GEOLOGICAL SURVEY Lower Hutt, NEw ZEALAND ABSTRACT New descriptions and figures are given for Pecten rigida Hall & Meek (= Pecten halli Gabb), the type species of Syncyclonema Meek, and for the type species of genera to which Syncyclonema is often compared: Entolium Meek, Eburneopecten Conrad, Pec- tinella Verrill, Hyalopecten Verrill, Camptonectes Agassiz, Micro- nectes Ichikawa & Maeda, Pseudamussium Morch, and ‘“Pseuda- mussium” H. & A. Adams. Syncyclonema is shown to be a valid genus. A lectotype is designated for Syncyclonema halli, and on the basis of its chlamyiid shape, deep byssal notch, and hinge morphology Syncyclonema is placed in the family Pectinidae. These characters invalidate synonymy of Syncyclonema_ with Entolium and its assignment to the family Entoliidae Korobkov. i) Postilla YALE PEABODY MUSEUM No. 110 INTRODUCTION Hall & Meek’s (1856, p. 381, pl. 1, figs. 4a-c) original description of Pecten rigida, the type species of Syncyclonema Meek (1864a), was brief and the accompanying figures rather indefinite. Consequently, the systematic position of Syncyclonema and its relationships to other genera have been confused and controversial. Staesche (1925, p. 90) considered Syncyclonema a distinct genus and a smooth chlamyiid with a very weak byssal notch. Verrill (1897, p. 62) hesitantly accepted Syncyclonema as a valid genus and compared it to his recent genus Hyalopecten. Syncyclonema was classed as a subgenus of Pecten by Woods (1902, p. 145), who also thought it was probably synonymous with Entolium (Meek, 1865, p. 478; type species by original designation, Pecten demissus Phillips, Middle Jurassic). Stephen- son (1941, p. 133) considered it of uncertain generic status, but included it as a subgenus of Pecten. Arkell (1930, p. 91) made Syncyclonema synonymous with Entolium to which he gave prior- ity. Stewart (1930, p. 120) and Feldtmann (1951, p. 10), who followed the same procedure, more correctly gave Syncyclonema priority. In contrast Hayami (1965) concluded that Syncyclonema is distinct from Entolium. Both Dall (1898, p. 752) and Cox (1952, p. 35) thought the genus too poorly known to be certain of its status. Because of the inadequacy of Hall & Meek’s (1856) original description of Pecten rigida for detailed systematic com- parisons the conclusions of Dall and Cox are the most correct. So much difference of opinion indicates the need for a rede- scription and discussion of the morphological features of P. rigida. The new data provides a base for considering the relationships between Syncyclonema and other similar small pectinid genera with which it has often been compared. ACKNOWLEDGEMENTS Comparison of Syncyclonema with other genera through the loan of material, provision of information, and discussion, has been facilitated by the following persons whose assistance is gratefully acknowledged: The late Dr. L. R. Cox, Mr. C. P. Palmer and Mr. N. J. Morris, British Museum of Natural History, London; Mr. A. G. Brighton, Sedgwick Museum, Cambridge; Dr. 1967 REVISION OF SYNCYCLONEMA | RV 3 J. M. Edmonds, University Museum, Oxford; Mr. G. F. Willmot, Yorkshire Museum, York; Dr. W. J. Clench, Museum of Com- parative Zoology, Harvard University, Cambridge, Massachusetts; Dr. Copeland MacClintock and Mr. Percy Morris, Peabody Mu- seum, Yale University, New Haven, Connecticut; Prof. N. D. Newell, American Museum of Natural History, New York, New York; Dr. C. F. Kilfoyle, New York State Museum, Albany, New York; Prof. H. G. Richards, Academy of Natural Sciences, Phil- adelphia, Pennsylvania; Drs. E. G. Kauffman and Joseph Rose- water, and Mr. W. J. Byas, United States National Museum, Washington, D.C.; Dr. Peter Rodda, Texas Bureau of Economic Geology, Austin, Texas; Prof. W. P. Popenoe, University of California, Los Angeles, California; Dr. Koichiro Ichikawa, Osaka City University, Osaka; and Dr. Itaru Hayami, Geology Depart- ment, Kyushu University, Fukuoka, Japan. Messrs S. N. Beatus and D. L. Homer took most of the photographs accompanying this paper. Doctors Kauffman and K. M. Waage, Peabody Museum, Yale University, and Dr. G. R. Stevens and Mr. P. A. Maxwell, New Zealand Geological Survey, kindly read the text and made valu- able suggestions. Specimens of Syncyclonema halli were collected and described as part of a dissertation for the Degree of Doctor of Philosophy at Yale University, while I was on leave from the New Zealand Geological Survey and was a holder of a New Zea- land Department of Scientific and Industrial Research National Research Fellowship. Specimens mentioned and figured in this paper are held at the following institutions: Academy of Natural Sciences, Philadelphia (ANSP) American Museum of Natural History (AMNH) British Museum of Natural History (BMNH) Museum of Comparative Zoology, Harvard University (MCZ) Osaka City University (OCU) Peabody Museum of Natural History, Yale University (YPM) Texas Bureau of Economic Geology (BEG) U. S. National Museum (USNM) World Mollusca Collection, New Zealand Geological Survey (NZGS-WM ) Yorkshire Museum 4 Postilla YALE PEABODY MUSEUM No. 110 DISCUSSION OF THE STATUS OF SYNCYCLONEMA AND ITS EYPE SPECIES PECLEN TArET HISTORY OF THE TYPE SPECIES OF SYNCYCLONEMA Meek (1864a, p. 31) proposed the genus Syncyclonema, with Pecten rigida Hall & Meek (1856, p. 381, pl. 1, figs. 4a-c; non Pecten rigida Sowerby, 1818, p. 5, pl. 205, fig. 8; = Pecten halli Gabb, 1861, p. 214), Upper Cretaceous, as the type species by original designation. Meek, on p. 31, used the spelling Syncyclo- nema in the heading to a short description and discussion of the genus as follows: “195 = SYNCYCLONEMA, Meek. Type Pecten rigida, Hall & Meek”, but on an earlicr page in a check list he (p. 7) used a second spelling, “195. Sincyclonema_rigida, (Hall & Meek) Meek. Dak.”. It is important to note that Meek used the spelling Syncyclonema in his generic description and designation. This spelling was used consistently by Meek in later publications and on labels accompanying collections he examined. Most other workers since Meek have preferred the spelling Syncyclonema. It is therefore concluded that the spelling Sincy- clonema was probably a typological or editorial error, and under the terms of the first reviser, Article 24 of the “ International Code of Zoological Nomenclature” (Stoll, et al., 1961), Syncy- clonema is designated as the valid spelling. Pecten rigida was erected by Hall & Meek (1856, p. 381) for a small pectinid collected by F. V. Hayden from the upper Pierre Shale at Sage Creek, South Dakota. Gabb (1861) noted the preoccupation of the name rigida by Pecten rigida Sowerby (1818), a quite different species, and renamed Hall & Meek’s species as Pecten hallii Gabb. Following the recommendation of the Inter- national Commission of Zoological Nomenclature (Stoll, et al., 1961, p. 107) the ending -i rather than -/i is used here. Gabb’s new name was ignored by Meek (1864a, p. 31) when he proposed the genus Syncyclonema, although he clearly knew that the name rigida was preoccupied and his species distinct from Sowerby’s. Meek (1876) later redescribed rigida and gave a more complete diagnosis of the genus Syncyclonema, but placed Gabb’s name halli in synonymy under his rigida. Since 1876 the only other work of importance discussing this species is that of Whitfield 1967 REVISION OF SYNCYCLONEMA 5 (1880) who described and illustrated specimens of S. halli (USNM 12272) from the Cheyenne River, Black Hills. Whitfield (1901, p. 424) reported that the American Mu- seum of Natural History held “the Gen. and Sp. Type. Syncyclo- nema Meek rigidum ... H. & M.”, from Sage Creek, Wyoming (AMNH 5351/1). The full label accompanying this collection, now numbered as AMNH 9347, lists “Syncyclonema_ rigida, Ee& Mesp: YPE. Mem A; Ac. Scic& Arts, vol. 5; p: 381, pl; fig. 4, Cretaceous No. 4, Fort Pierre Gp. Sage Creek, Nebraska (Wyoming).” Professor N. D. Newell kindly examined the col- lection and reported (written communication Oct. 17, 1966) that the specimens of S. halli “do not agree in detail with the original figures” of Hall & Meek. Comparison of photographs (pl. 1, figs. 1-3) of right and left valves most closely resembling Hall & Meek’s drawings, here reproduced as figs. 6 and 7, pl. 1, support Profes- sor Newell’s conclusion. Hall & Meek’s drawings were probably idealized by the artist, especially as the specimens are small. Gross similarities are evident, but differences in size, shape and orna- ment make it impossible to be sure that the specimens in AMNH 9347 are the originals from which the drawings were made. Because Hall & Meek’s original collections were dispersed I examined collections at the United States National Museum, Washington, and the Academy of Natural Sciences, Philadelphia, but found no specimens matching the original drawings. Collec- tion USNM 347 is listed (Schuchert, 1905, p. 636) as containing “Cotypes” of S. halli. As this collection is from “The Cheyenne and Moreau Rivers, South Dakota”, and not from Sage Creek, it cannot be the original collection of Hall & Meek. Consequently, the specimens of S. Aalli in this collection are not cotypes but probably include all or some of the specimens on which Meek (1876) based his redescription of the species and possibly his figures (1876, pl. 16, figs. 5a, b; but see below). Correspondence with Dr. Kilfoyle, New York State Museum, Albany, and Pro- fessor Popenoe, University of California, Los Angeles, established that these institutions do not hold collections likely to contain Hall & Meek’s original specimens of S. halli. Collection USNM 347 includes three specimens of S. halli; a left valve (347a), a partly buried valve with concentric sculpture (347b), and a partly buried interior showing fine radial striae (347c). 6 Postilla YALE PEABODY MUSEUM No. 110 Specimen 347a is labeled as being the original of fig. 5b of the pl. 16 of Meek (1876) (pl. 3, fig. 4). But this specimen, and also the drawing, is a left valve and not a right valve as stated in Meek’s caption. Judging from his descriptions Meek (1876, p. 27) probably mixed the captions of his figures Sa and 5b. In addition, correspondence of the specimen with fig. Sb is unlikely because the specimen retains most of the shell on the ventral half of the valve, and it lacks the fine radial striae and widely spaced concentric ornament shown on Meek’s illustration of the steinkern (pl. 1, fig. 4). The differences are too great to be accounted for by artistic license, for even though Meek idealized many of his illustrations to varying degrees, he usually recorded gross morphological characteristics and imperfections. In many cases I have been able to identify positively Meek’s specimens because of imperfections recorded on the drawings. Althougi USNM 347a is unlikely to be the original of fig. 5b, the original specimen should be located to prove positively this contention. There is no trace of the original of Meek’s (1876, pl. 16) fig. 5a in USNM 347, and this specimen also appears to have been lost. Although it is not possible to be absolutely certain that the specimens represented by the original illustrations of Hall & Meek are conspecific with the specimens of S. halli in AMNH 9347 their gross similarity strongly suggests that they are conspecific (see pl. 1, figs. 1-3, 6, 7). Examination of Meek’s (USNM 347) and Whitfield’s (1880, USNM 12272, pl. 1, fig. 8) specimens shows they are conspecific with each other and also with the specimens in AMNH 9347 and collections made by Professor K. M. Waage and myself from the type area of the Fox Hills Formation. Meek’s identification and labeling as Pecten rigida of specimens in USNM 347, which were collected from the “Chey- enne and Moreau Rivers’, a locality lying within the type area of the Fox Hills Formation, gives additional support to my conclu- sion that Hall & Meek’s species concept includes the specimens in the collections discussed above. No holotype or lectotype has been designated for S. halli. In order to fix the concept of the species, and genus, it is neces- sary to select a lectotype. Although it can never be certain that AMNH 9347 is the original collection studied by Hall & Meek, 1967 REVISION OF SYNCYCLONEMA 7 or that it contains the originals of their illustrations, all the evi- dence indicates that it most probably is the original collection. Consequently, the almost complete right valve (AMNH 9347/1.1; pl. 1, fig. 3) from this collection, 4 mm long and 5 mm high, showing nine shallow concentric plicae on the ventral half of the shell, and a distinct byssal notch, but with the anterior auricle incomplete, is here selected as the lectotype. SYSTEMATICS OF SYNCYCLONEMA AND ITs TYPE SPECIES GENUS SYNCYCLONEMA AUTHOR. Meek, 1864a, p. 31, 7. TYPE SPECIES. By original designation, Pecten rigida Hall & Meek (1856, p. 31, pl. 1, figs. 4a-c; non Pecten rigida Sowerby, 1818, p. 5, pl. 205, fig. 8; = Pecten halli Gabb, 1861, p. 214), Sage Creek, South Dakota, Pierre Shale, Upper Campanian-Maastrich- tian. EMENDED DIAGNOSIS OF SYNCYCLONEMA. The following diag- nosis is based on study of the type species halli (see below): Small, subequivalve, subequilateral. Shell of vitreous appear- ance, thin, of three layers: thin outer homogeneous or prismatic layer, middle layer of zigzag lamellar structure, and thin inner complex cross-lamellar layer. Ornament sub-macroscopic, except on ears, of fine non-punctate diverging radial striae, fine growth striae, and coarser irregular growth lamellae tending to give reticulate pattern. Radial striae strongest at ventral margin and on dorsal flanks of disc of shell, sometimes absent on center of disc. Concentric lamellae strong on ears. Interior of shell sometimes with low faint rounded concentric ridges and fine radial striae. Concentric undulations sometimes evident on external surface, particularly on the right valve. Anterior auricle equal to or significantly larger than the poste- rior. Anterior auricle of the right valve distinctly separated from disc of shell, fasciole very narrow, and byssal sinus deep, open V-shaped. No ctenolium. Dorsal margin of right valve overlaps that of the left valve. Each auricle with one thin cardinal crus below the ligament band, that on the posterior auricle of each 8 Postilla YALE PEABODY MUSEUM No. 110 valve extending usually only about two-thirds of the distance to- wards the posterior margin (pl. 3, figs. 1, 5). One relatively long strong tooth-like process on either side of the resilifer pit of the right valve (pl. 2, fig. 5; pl. 3, figs. 2, 5). No auricular crura. Adductor muscle impression small, subcircular, sited above two- thirds the height of shell adjacent to basal part of posterior auricle. Pallial line continuous. DISCUSSION. Several morphological features of the type species, S. halli, require discussion before the status of Syncyclonema is fully clarified. 1. Byssal sinus. Syncylonema halli has a deep byssal sinus on the right valve (pl. 2, figs. 1, 5). Careful examination of the internal and external surfaces of right valves provided no evidence of a ctenolium at any stage of growth. S. halli was prob- ably a free swimming pectinid. Stewart (1930, p. 120) thought the small specimens of S. halli described by Hall & Meek (1856) and Meek (1876) might be juveniles of a species of Entolium, but growth lines show the presence of a relatively large byssal auricle at all stages of growth, and for this reason S. halli cannot be classed in Entolium (see below). The normal occurrence of specimens 10 to 13 mm long, but none larger than this, suggests that the largest specimens are adults of a small species. 2. Musculation. The adductor muscle impression is weakly impressed and was observed on only a few specimens. It is small, subcircular, sited postero-dorsally, with its base at or above two- thirds of the height of the shell adjacent to the basal part of the posterior ear (pl. 2, fig. 3; pl. 3, fig. 6). Whitfield (1880, pl. 7, fig. 1) illustrated the adductor scar which, as he noted, occurs in an unusual position. Examination of his specimen (USNM 12272; pl. 1, fig. 8) shows that the impression is partially masked by a pattern of vermiculated markings. The pallial line sometimes coinicides with the contact of the inner and outer shell layers and has a small oval inflated impression near its postero-ventral extremity (pl. 3, fig. 6). 3. Auricular crura. No auricular crura are developed, although a few right and left valves have the internal surface of the anterior ear slightly thickened along the junction with the main disc of the shell. 1967 REVISION OF SYNCYCLONEMA 9 4. Ornament. Meek (1864a, p. 31), in his original diagnosis of the genus, described the ornament of the right and left valves as “surface with fine obscure concentric striae and sometimes on the right valve, small rounded concentric ridges.” In his (Meek, 1876, p. 26) later, more detailed diagnosis he stated “surface showing only concentric striae, and sometimes stronger, regularly defined concentric ridges on the right valve.” Although he uses the word “sometimes” in this description, on p. 27 he stressed the discrepancy of ornament between the valves. In their original description of S. halli Hall & Meek (1856) described but did not emphasize the discrepancy in ornament. Clearly the emphasis should have been on the similarity of the ornament on each valve, and on the uncommon occurrence of weak concentric plicae. Misinterpretation of Meek’s diagnosis and discussion has undoubtedly contributed to the uncertain status of the genus. Most of the specimens from the Fox Hills Forma- tion, admittedly younger stratigraphically than those of Hall & Meek (1856) from Sage Creek, have similar ornament on each valve. Weak concentric ridges are sometimes present on the inner surface of the shell of either valve (pl. 3, fig. 4), and tend to show up more strongly on steinkerns. Strong concentric lamellae are rarely developed. The lamellate ornament, like the internal concentric ridges, tends to be accentuated by the removal of the thin outer prismatic layer of the shell. The concentric ridges are more regular on the steinkern illus- trated by Whitfield (1880, pl. 7, fig. 1; see pl. 1, fig. 8), and on the right valves in AMNH 9347 (pl. 1, figs. 1, 3), than on any specimen collected from the type area of the Fox Hills Formation. Compared with the overall similarity of the other morphological features, the difference in this one character is not considered of species rank, particularly as the concentric ridges are stronger on small than large specimens (compare pl. 1, figs. 1, 3, 8, with pla, fig. 4). COMPARISONS. Other virtually smooth small pectinids assigned to Pecten, Camptonectes, and Syncyclonema, may also be con- generic with S. halli. Possible Upper Cretaceous species include Pecten (Camptonectes) kaufmanensis Stephenson (1941, pl. 21, figs. 7-9), P. (C.) cavanus Stephenson (1952, pl. 19, fig. 7), P. 10 Postilla YALE PEABODY MUSEUM No. 110 (Syncyclonema) travisanus Stephenson (1941, pl. 22, fig. 1), and specimens placed under Pecten simplicius Conrad (e.g. Wade, 1926, pl. 20, fig. 7). Inclusion of these species would necessitate modifying the diagnosis to cover species with ornament varying from smooth to with strong concentric striae, with the byssal notch deep to moderate, and the fasciole narrow to moderately wide. Syncyclonema halli (Gabb) (Pl. thes. 1-95 pl. 2; figs. 1=55ple 35 fies: 1-4 254-bp Pecten rigida Hall & Meek, 1856, p. 381, pl. 1, figs. 4a-c (non Sowerby, 1818, p. 5, pl. 205, fig. 8). Pecten hallii Gabb, 1891, p. 214. (Nom. nov. for P. rigida Hall & Meek). Sincyclonema rigida (Hall & Meek). Meek, 1864a, p. 7. Syncyclonema rigida (Hall & Meek). Meek, 1864a, p. 31. Meek, 1876, p: 27, pl. 16, figs. 5a, b. Whitheld; 1880; pa3sae ple 7, tig. A: LECTOTYPE. Here selected (p. 7), AMNH 9347/1.1, a right valve, 4 mm long and 5 mm high (pl. 1, fig. 3), Sage Creek, South Dakota, Pierre Shale, Upper Campanian-Maastrichtian. MATERIAL. One hundred and seventeen specimens, including eight articulated or displaced bivalved. OCCURRENCE. In the type area of the Fox Hills Formation S. halli is virtually restricted to the Timber Lake Member (Waage, in press). The species, recorded by Fisher, et al. (1960), as Syncyclo- nema hallii, from the lower part of the Pierre Shale and in the Sego Sandstone in western Colorado and eastern Utah, and by Griffitts (1949) as S. rigida, from the “Rocky Ridge sandstone member of the Hygiene zone” of the Pierre Formation in Colorado, is apparently rare in the Upper Cretaceous sequences of the Western interior. It is found mainly in sandstone units. DESCRIPTION. Small, length of specimens 3.5 to 13.2 mm, subequi- valve, equilateral to slightly inequilateral, compressed, valves equally inflated. Orbicular, with height, width of one valve, length 1967 REVISION OF SYNCYCLONEMA ial of dorsal margin (between extremities of ears), and anterior lenothyrespectively, 1OI4 ton1292 (n=287 x11. 7%), 4:6. t0 131325) x— 911%), 482) 1064.6. (n= NOY x=5 4.9%). and 45 to 55.9 (n=28, x=49.2% ) per cent of length, and length of anterior ear 50 to'63.2) (n=19, x=55.7-% ) per cent of length of dorsal margin. Umbones weakly prosogyrous, project slightly above dorsal margin. Antero- and postero-dorsal margins of the disc of shell straight or slightly concave, form an angle of 87.5 to 100 degrees, and meet the rounded ventral margin at distinct angula- tions. Dorsal margins of ears straight, intersect at a small angle, the anterior is more steeply inclined. Margin of right valve, espe- cially that of the anterior ear, projects above and overlaps the margin of left valve. Anterior ear equal to or larger than posterior. Ears of left valve, and posterior ear of right valve, weakly delimited from disc of shell, although the margin of disc becomes overhang- ing ventrally, with straight or rounded anterior or posterior margins which form a rounded or angled junction with the dorsal margin of the ear. Anterior ear of right valve sharply delimited from the overhanging margin of the disc, with a narrow fasciole at base, at the ventral end of which is a narrow moderately deep V-shaped byssal sinus. Ctenolium apparently lacking. Ornament similar on both valves, of submicroscopic vermiculat- ing Camptonectes-striae, 40 to 50 per millimeter at ventral margin, fine growth striae and coarser irregular growth lamellae tending to give a reticulate pattern. Striae are sometimes very weak on the center of disc and, with the growth striae, are often very strong on the antero- and posiero-dorsal flanks of disc and some- times on ears. Either the striae or growth lamellae may dominate on the ears. Internal surface of shell sometimes with irregular or regular shallow rounded concentric costae and fine radial striae. Resilifers triangular, internal, do not extend to ventral margin of hinge-plate. Resilifer of right valve bordered on either side by a short strong tooth-like process which extends the length of the resilifer and fits into sockets on each side of the resilifer of the left valve. Ligament groove narrow, submarginal, extends most of length of ears, bordered below by a weak cardinal crura. No auric- ular crura. Pallial line continuous, extending in a loop across shell at about one-quarter of the height above base, becomes indefinite antero-dorsally at base of the fasciole. The pallial line has a smali 1 Postilla YALE PEABODY MUSEUM No. 110 subquadrangular scar situated at about one-third the height of the shell; and a large subcircular adductor scar is situated near the base of the posterior ear in the dorsal quarter of the shell. Muscle scars on the left valve unknown. Ostracum less than 0.2 mm thick, of three layers. A very thin outer layer, probably prismatic, bearing the Camptonectes striae, a translucent middle layer, apparently of zigzag lamellar structure (Béggild, 1930, p. 267), that thickens towards the ventral margin, and an inner white layer of complex cross-lamellar structure that is thickest in the umbonal region and ceases within one to two millimeters of ventral margin (pl. 2, fig. 1). Outer surface vitreous, but with irregularly distributed, radially elongated patches of matt appearance (pl. 2, fig. 4). DISCUSSION. Left and right valves of S. halli are equally inflated and their other measurements have approximately the same range of values and means. In spite of the extremely fragile shell few specimens from concretions in the type area were broken during deposition. Complete specimens are very difficult to extract and the ears are especially prone to damage. At Yale loc. 288, Solen, North Dakota, where the sediment is a limonite-cemented medium-grained sandstone with little argillaceous matrix, many specimens were broken during transportation. The tripartite layer- ing of the shell described above requires confirmation by thin section studies. As interpreted it is similar to the shell of “P. textorius (Liassic)” of Bgéggild (1930, p. 267). The very thin outer prismatic layer bears the Camptonectes-like striae and, although always present on well preserved specimens, it is easily removed by abrasion, weathering or extraction. The shell then appears smooth or with concentric lamellae only. Species of Camptonectes recorded in the literature as being smooth and striate should be re-examined to ascertain that the outer layer, if this is characteristic of the genus, has not been lost, especially in the case of small species. Whitfield (1880, pl. 7, fig. 1) illustrated a different pattern of muscle scars on a steinkern from “the forks of the Cheyenne River, Black Hills.” He commented on the unusual position of the muscle scar. Examination of recent pectinid species held in the collections of the Peabody Museum, Yale University, showed 1967 REVISION OF SYNCYCLONEMA 13 that some, for example Cyclopecten (Delectopecten) vitreus (Chemnitz), Pseudamussium striatum (Miller), and P. septem- radiatum (Miller), have an elongated or oval scar in a com- parable position close to the base of the posterior ear of the right valve. The ventral small subquadrangular scar in the pallial line is present on several specimens and seems to be a valid scar. It may represent a gill suspensory attachment (Newell, 1937, p. 21). COMPARISONS. Specimens of Pecten (Camptonectes) kaufmanensis Stephenson (1941, pl. 21, figs. 7-9) and P. (C.) cavanus Stephen- son (1952, pl. 19, fig. 7) closely resemble S. halli. Other speci- mens from Gulf and Atlantic Coastal Plains sequences classed under Pecten or Syncyclonema resemble S. halli in shape and size but apparently lack the fine Camptonectes-striae. Some, for exam- ple P. (Syncyclonema) travisanus Stephenson (1941, pl. 22, fig. 1), show traces of radial ornament, while others, like P. simplicius Conrad (Wade, 1926, pl. 20, fig. 7) and the right valve of P. travisanus (Stephenson, 1941, pl. 22, fig. 2), have relatively strong lamellae like S. halli when its outer prismatic layer is lost. THE FAMILY PLACEMENT OF SYNCYCLONEMA Pectinid-like genera have been classified into either the Pectinidae Rafinesque (1815) or the Amusiidae Ridewood (1903). The placing of genera in the Amusiidae is primarily based on anatomy (Cox, 1952, p. 33), and in the absence of anatomical information the classification of some fossil and Recent genera is difficult, especially small, thin-shelled, weakly ornamented forms which possess a small byssal notch and lack internal ribs and muscle impressions. Most paleontologists have accepted only one family, the Pectinidae (Marwick, 1928; Grau, 1959). Newell (1965, p. 18) follows this procedure in his proposed classification of the Bivalvia for the “American Treatise of Invertebrate Paleontology.” Korobkov (1960) subdivides the Pectinidae into five sub- families, including the Amusiinae and Pectininae. Detailed revi- sion of the morphology and anatomy of pectinid genera is required 14 Postilla YALE PEABODY MUSEUM No. 110 to confirm the validity of some of these subfamilies. A new sub- family proposed by Korobkoy, the Entoliinae, was raised to family rank by Newell (1965). Characteristics of the family include an equivalve or subequivalve inflated shell, weak orna- mentation, a small or no byssal sinus, and usually strong auricular and cardinal crura. The following is a translation of the diagnosis of the subfamily Entoliinae given by Korobkov (p. 83) as pre- pared by the Translation Service of the New Zealand Department of Internal Affairs: “The shell is prosocline or acline, often gaping; the ears of the left valve are raised, those of the right valve are almost identical and not raised, the resilifer cavity is almost symmetrical and com- paratively small; dentate ridges are strongly developed on the ears, at their base they appear more weakly; the byssus notch is entirely absent or can be seen only in the early stages of develop- ment; the outer surface is smooth or has regular concentric riblets, more rarely having radial striae. Carboniferous to Cretaceous.” Genera included by Korobkov in the Entoliinae are Perno- pecten Winchell (1865), Entolium Meek (1865), and doubt- fully Syncyclonema Meek (1864a). Other possible members are Pseudentolium Cox (1948; not synonymous with Eburneopecten as suggested by North, 1951) and Creniopleurium Feldtmann (1951). Somapecten Kimura (1951), Jurassic, should perhaps be included, although it has a distinctive interlocking hinge appa- ratus and may be an aberrant offshoot of a pectinid or entoliid stock. Recognition of the Pectinidae and Entoliidae separates two morphologically different groups of genera, chlamyiid-like and entoliid-like respectively, and is supported by the writer. Detailed paleontological studies are required to prove whether the Entoli- idae is monophyletic or polyphyletic. The occurrence throughout the late Mesozoic and Tertiary of pectinid genera, e.g. Lentipecten Marwick (1928), and amusiid-like genera, closely resembling entoliids suggests that the Entoliidae may be polyphyletic and include convergent end members of branches from a pectinid stem. The morphology of Syncyclonema indicates placement in the Pectinidae and clearly excludes it from the Entoliidae, as is shown in the next section. 1967 REVISION OF SYNCYCLONEMA 15 ENTOLIUM, AND A COMPARISON WITH SYNCYCLONEMA GENUS ENTOLIUM AUTHOR. Meek, 1865, p. 478. TYPE SPECIES. By original designation, Pecten demissus Phillips (1829, p. 124, 140, pl. 6, fig. 5), Middle Jurassic, England and Europe. DISCUSSION. Diagnoses of the genus Entolium (Arkell, 1930, p. 91; Cox, 1952, p. 34) stress external morphological features, especially the relatively smooth thin shell, dorsally projecting auricles (particularly on the left valve), and the lack of a byssal notch (at least on adult specimens). The external characteristics as shown by the holotype of E. demissum (pl. 3, fig. 3) are rather constant, although the shape of a species may be extremely variable (Staesche, 1925, p. 100). Less is known of the internal features of species of Entolium. One of the three groups of Staesche (1925), that of E. cingulatum Goldfuss, has fine internal ridges on the main disc of the shell close to each auricular margin. The generic significance of these ridges is uncertain. Most species possess strong auricular crura and one cardinal crus on each auricle close to the dorsal margin (Korobkov, 1960, p. 83; E. sanchuense, Hayami, 1965, p. 315; E. fossatum, Marwick, 1953). The auricular crura in part reflect the strong grooves which separate the auricles from the disc of the shell on many species. Some species appear to lack cardinal crura, although others have two strong cardinal crura on the right valve (E. irense McLearn, 1933, pl. 1, fig. 10; NZGS-WM 5403) or possibly two crura and tooth-like processes on each side of the resilifer, [E. orbicularis (Sowerby) Woods, 1902, pl. 27, fig. 14]. I attempted to obtain suitable specimens to clarify the hinge morphology of the type species E. demissum. Unfortunately, these were not available from the collections of the British Museum, Oxford University, or Cambridge University. Consider- able work is required before the taxonomy of entoliids is clear. 16 Postilla YALE PEABODY MUSEUM No. 110 COMPARISON OF ENTOLIUM with SYNCYCLONEMA. Many authors, as summarized in the Introduction (p. 2), have sug- gested synonymizing Syncyclonema under Entolium. The inade- quacy of the original descriptions and illustrations of S. halli undoubtedly has led workers to assume that it had approximately equal auricles and lacked a distinct byssal sinus. Nevertheless, Syncyclonema is easily distinguished from Ento- lium by its chlamyiid rather than orbicular shape, the possession of a deep byssal sinus, which is lacking on Entolium, and the occurrence of radial ornament on the auricles, which is also not present on Entolium. Internally, Entolium lacks the distinct tooth- like processes present on either side of the resilifer on the right valve of Syncyclonema. Other differences in internal morphology, for example musculation, may prove to be significant. The differences prove that Syncyclonema should not be syno- nymized under Entolium. COMPARISON OF SYNCYCLONEMA WITH OTHER SMALL PECTINID GENERA Syncyclonema superficially resembles a number of pectinid genera and this similarity has been a source of confusion. In particular, Syncyclonema has been compared with Camptonectes Agassiz, Eburneopecten Conrad, Pectinella Verrill, Micronectes Ichikawa & Maeda, Hyalopecten Verrill, and Pseudamussium (see below). Study of these genera has been hampered by a lack of knowl- edge of morphological features and variation within the genera, particularly as most of the genera are known largely from the type species. Shape and ornament are the characters used to separate most pectinid genera. Poorly known and little used morphological features of potential systematic importance include shell struc- ture, details of muscle impression patterns, hinge morphology — especially the number and length of the cardinal crura and whether or not the dorsal one bears the ligament— and the consistency and length of the tooth-like process on either side of the resilifer of the right valve. 1967 REVISION OF SYNCYCLONEMA 11 7/ To facilitate comparison of several of the above genera with Syncyclonema the opportunity is taken in the following sections to redescribe the type species of the poorly known genera Pec- tinella, Hyalopecten, Pseudamussium Morch, and “Pseudamus- sium” H, & A. Adams. The formal systematic data for the genera and their type species are presented and discussed where appro- priate. Presentation of full synonymies of the type species is not practicable for this paper. 1. GENUS CAMPTONECTES AUTHOR. Agassiz, in Meek, 1864b, p. 28, 39. TYPE SPECIES. By original designation, Pecten auritus Schlotheim (1813; = P. lens Sowerby, 1818), Middle and Upper Jurassic, England and Europe. DISCUSSION. The authorship of Camptonectes is controversial. Meek (1864b, p. 39) clearly indicates that the concept of the genus, and the virtual selection of a type species, was due to Agassiz (MS) and under the Rules of Zoological Nomenclature (Stoll, et al., 1961, p. 49, Art. 50) the name should be accredited to Agassiz. Stoliczka (1871, p. 425) was the first to use the word type with reference to P. lens. COMPARISON WITH SYNCYCLONEMA. Typical small and large species of Camptonectes are clearly distinguished from Syncyclo- nema by their macroscopic and frequently punctate (but see Cox, 1952, p. 22) “Camptonectes’” ornament, large byssal ear with a wide fasciole, very deep byssal sinus, strong ctenclium, and thick shell (see pl. 4, fig. 3). The internal features of species of Camptonectes are poorly known. Cox (1952, p. 22) states that cardinal crura are lacking on the type species C. auritus, but they are present on Pecten (Camptonectes) moodyi Stephenson (1952, p. 79). A small specimen of C. auritus, prepared for the writer by Dr. L. R. Cox and his assistant, Mr. C. P. Palmer, shows a weak cardinal crus on each auricle of the right valve (pl. 4, figs. 1, 3). On the internal surface of the byssal auricle this specimen also has a 18 Postilla YALE PEABODY MUSEUM No. 110 strong ridge extending in an arc from the umbone to the antero- ventral margin of the auricle. This ridge is strongest antero- ventrally and coincides on the external surface with the dorsal margin of the wide fasciole. Dr. Cox (written communication, June 29, 1965) describes the hinge features as follows: “There is a very weak cardinal crus on each side close to the hinge margin and best developed some distance from the beak. In addition, there is a strong ridge running from the beak to the lower margin of the part of the anterior auricle above the byssal notch. This ridge is also well seen in a second specimen. A comparable but weaker ridge is present in some Recent specimens of Chlamys. Auricular crura, running from the beak along the lower margin of complete auricles, are absent.” The anomaly of no crura on some specimens and weak crura on small specimens may be accounted for by the degeneration and loss of crura with increas- ing size and age. The general position of many small, weakly ornamented, species placed in Camptonectes is uncertain. Some may belong to Micronectes and others to Syncyclonema. 2. GENUS EBURNEOPECTEN AUTHOR. Conrad, 1865, p. 140. TYPE SPECIES. By monotypy, Pecten scintillatus Conrad (1865, p. 140, pl. 10, fig. 4), Moodys Branch Marl, Jackson Group, Upper Eocene, Garlands Creek, Clarke County, Mississippi. COMPARISON WITH SYNCYCLONEMA. Externally Syncyclonema very closely resembles species of Eburneopecten, which differ significantly only by the presence of a strong ctenolium, prominent radial costae, a more distinct fasciole on the anterior ear of the right valve, and less prominent lamellae on the auricles. The dis- covery by Stenzel, et al. (1957, p. 85), of specimens of Eburneo- pecten lacking radial ornament on the anterior auricle suggests that this feature may be of specific rank only. Eburneopecten differs from Syncyclonema mainly in internal morphology. Eburneopecten has two cardinal crura on each auricle of the right valve and on the anterior auricle of the left valve, PLATE SECTION PEATE 1 Syncyclonema halli (Gabb) Fic. 1. Syntype, AMNH 9347/1.2. Exfoliated right valve, anterior auricle incomplete. Pierre Shale, Sage Creek, Upper Cretaceous. x 10. Fic. 2. Syntype, AMNH 9347/1.3. Incomplete steinkern of a left valve. Pierre Shale, Sage Creek, Upper Cretaceous. « 10. Fic. 3. Lectotype, AMNH 9347/1.1, here selected. Right valve with an incomplete anterior auricle. Most of shell removed, remainder lacking outer shell layer. Pierre Shale, Sage Creek, Upper Cretaceous. x 10. (Photographs for figs. 1-3 kindly supplied by Prof. N. D. Newell). Fic. 4. Fig. 5b of Meek (1876, pl. 16), a left valve and not a right valve as stated in the caption. Supposedly in USNM 347, Pierre Shale, Cheyenne and Moreau Rivers, South Dakota, Maastrichtian. Not found, assumed lost. * ca. 2. Fic. 5. Fig. 5a of Meek (1876, pl. 16), a right valve and not a left valve as stated in the caption. Anterior auricle probably incomplete. Supposedly in USNM 347, not found, assumed lost. * ca. 2. Fics. 6, 7. Figs. 4c and b respectively of Hall & Meek (1856, pl. 1), left and right valves respectively. Pierre Shale, Sage Creek, Upper Cre- taceous. < ca. 2. (Photographs kindly supplied by John Howard, Peabody Museum, Yale University). Fic. 8. USNM 12272; steinkern of a right valve, anterior auricle incomplete, showing concentric ridges and fine radial striae. The original of Whitfield, 1880, pl. 7, fig. 1. Forks of the Cheyenne River, Black Hills, South Dakota, Upper Cretaceous. 6. Fic. 9. YPM 24129; a left valve from Solen, North Dakota, YPM colln. A-1409, loc. 288, Timber Lake Member, Fox Hills Formation, Maastrichtian. « 6. PLATE 2 Syncyclonema halli (Gabb) Fic. 1. YPM 24122; an internal view of the shell of a right valve, showing the inner thin white complex cross-lamellar layer and the trans- lucent middle layer. Note the deep byssal notch and incomplete cardinal crus on the anterior auricle. YPM A-650, loc. 73, Cucullaea Assemblage Zone, Timber Lake Member, Fox Hills Formation, Maastrichtian. «x 6. Fic. 2. YPM 24126; a left valve showing ornament on the auricles and fine diverging radial striae on the margins of the disc. YPM A-1409, loc. 288, Solen, North Dakota, Timber Lake Member, Fox Hills Formation. <9! Fic. 3. ANSP 31245; internal view of the postero-dorsal part of the shell of a right valve showing the faintly impressed adductor muscle impres- sion close to the base of the posterior auricle. Pierre Shale, Mingusville. Montana, collector Homer Squyer, Upper Cretaceous. « 12. Fic. 4. YPM 24127; a left valve showing ornament, particularly the diverging radial striae on the margins of the disc. YPM A-1409, loc. 288, Solen, North Dakota, Timber Lake Member, Fox Hills Formation. « 9. Fic. 5. YPM 24123; interior of dorsal part of a right valve, the ante- — rior auricle incomplete and centre of hinge damaged, showing cardinal crura. YPM A-973, loc. 100, Cucullaea Assemblage Zone, Timber Lake Member, Fox Hills Formation. « 12. PLATE, 3 Syncyclonema halli (Gabb) Fic. 1. YPM 24124; rubber latex cast of a left valve hinge showing cardinal crura, resilifer, and lack of auricular crura. YPM A-659, loc. 73, Cucullaea Assemblage Zone, Timber Lake Member, Fox Hills Formation. SS 1 Fic. 2. YPM 24125; right valve hinge, anterior ear and dorsal part masked by matrix, showing tooth-like projections on each side of a narrow resilifer and the lack of ctenolium. YPM A-747, loc. 226, Cucullaea Assemblage Zone, Timber Lake Member, Fox Hills Formation. x 12. Fic. 4. YPM 25635; right valve steinkern with some exfoliated shell ventrally, showing radial striae and weak concentric ridges. YPM A-447, loc. 210, Cucullaea Assemblage Zone, Timber Lake Member, Fox Hills Formation. x 3. Fic. 5. USNM 347; rubber latex cast of a left valve, supposedly the original of Meek, 1876, pl. 16, fig. 5b, a right valve, showing cardinal crura and resilifer. Compare with pl. 1, fig. 4. Pierre Shale, Cheyenne and Moreau Rivers, South Dakota. x 4. Fic. 6. ANSP 31241; a right valve steinkern showing postero-dorsal adductor scar, pallial line, and postero-ventral swelling. Mingusville, Mon- tana, collector Homer Squyer, Pierre Shale. « 12. Entolium demissum (Phillips) Fic. 3. Holotype, Yorkshire Museum 202. Kellaways Rock, near Scarborough, Lower Callovian, Middle Jurassic. « 1. PLATE 4 Camptonectes auritus (Schlotheim ) Fics. 1, 3. BMNH LL 2445; internal views taken under different lighting of the interior of a right valve, showing ctenolium, weak cardinal crura and ridge extending from umborie to antero-ventral extremity of the byssal auricle. Malton, Yorkshire, probably from a “large stone quarry, Coralline Oolite, Upper Oxfordian, Zone of Perisphinctes plicatilis’ (L. R. Cox, letters Ames 2511965) =< 129: Fic. 6. BMNH LL 2445; exterior of right valve. Note wide byssal notch and fasciole, and punctate “Camptonectes’ ornament. Locality data as above. x 1.8. (Photographs for figs. 1, 3, 6, kindly supplied by Dr. Laken COX) Eburneopecten scintillatus (Conrad ) Fics. 2, 4. Topotype, BEG 20726; photographs of the exterior, fig. 2, and interior, fig. 4, of a right valve showing byssal notch, narrow fasciole, ctenolium, radial costae on the byssal auricle, weak auricular crura, cardinal crura, short tooth-like processes on each side of the resilifer, and the dorsally projecting dorsal margin. Garland’s Creek, Moodys Branch Marl, Jackson Group, Upper Eocene (see Stenzel, et al., 1957, p. 82). Bigs ara niger4a SC 6; Fics. 5, 7. Topotype, BEG 20725; photographs of the interior, fig. 5, and exterior, fig. 7, of a left valve showing weak auricular crura, cardinal crura with finely striated areas on each side of the resilifer, and large subcentral adductor scar. Locality data as above. Fig. 5, x 6; fig. 7, & 4. PLATE 5 Micronecies bellaturus Ichikawa & Maeda Fic. 1. OCU MM 2339; plastic cast of the dorsal part of a right valve showing strong radial costae on byssal auricle. Loc. 151, Azenotani — 3, Izumi Mountains, Azenotani Shale. Hetonian Series (Campanian). x 4. Fics. 2, 3. OCU MM 238; plastic casts of the exterior, fig. 2, and interior, fig. 3, of a left valve, showing ornament, cardinal crura, and dorsal triangular flat-surfaced “crura”. Locality data as above. x 6. Fic. 4. OCU MM 239; plastic cast of a right valve showing cardinal crus on the anterior auricle. Area around resilifer poorly preserved. Locality data as for fig. 1. x 6. Fics. 5, 7, 8. OCU MM 772; plastic casts of a right valve showing large anterior auricle, deep byssal notch, wide fasciole, strong costa directly above fasciole, the hidden ctenolium (fig. 7), the prosoclinal shape, resilifer and cardinal crura. Loc. 115, Takinoike, Izumi-Sano City, Osaka Prefec- ture, K. Ichikawa collector, 1962, Azenotani Shale. Fig. 5, 4; fig. 7, x 8. Fics. 6, 9. OCU MM 246; plastic casts of a valve possibly the left, the photographs taken under different lighting, to show ornament. Locality data as for fig. 1. x 4. PLATE 6 Pectinella sigsbeei (Dall) Fics. 1, 4. Holotype, MCZ 7817; a right valve, the anterior auricle incomplete, not whitened, showing shape, ornament, and hinge morphology. From “off Havana’, Recent. Fig. 1, 5; fig. 4, « 10. (Photographs kindly supplied by Dr. W. J. Clench). Fics. 2, 3. USNM 62263; a left valve, labeled as “type fig.’d”, and probably the matching valve of MCZ 7817, showing shape, ornament, cardinal and auricular crura. Lat 22°10’ N, long. 82°20’ W, depth 158 fms, Recent3)<2:8: Fics. 5, 6, 7. USNM 503313; a left valve, showing shape, ornament, cardinal and auricular crura. Off English Harbor, Antigua Is., 120 fms, rough coral, Recent. Figs. 5, 7, & 2.8; fig. 6, 4. Hyalopecten dilectus Verrill & Bush Fics. 8, 9. Holotype, USNM 44827; matching valves, showing shape, ornament, auricles and byssal notch. Stn 229, 1423 fms, off Maryand, Recent <2. PLATE 7 Hyalopecten dilectus Verrill & Bush Fics. 1, 2. Holotype, USNM 44827; matching valves, showing hinge morphology, byssal notch and ctenolium. Stn 229, 1423 fms, off Maryland, Recent. « 4. “Pseudamussium” hybridum (Gmelin) (type species of Pseudamussium H. & A. Adams) Fics. 3, 4, 8. USNM 131671; a small left valve showing ornament, hinge morphology, and adductor muscle scar. From West Africa, Lea col- lection, labeled as “probably Pecten dispar Lam.” by Dall?, Recent. Bich se eZ ign. as: Fics. 5, 6. USNM 131671; internal and external photographs of a right valve. Note ornament, hinge morphology and ctenolium. Locality data as above. X 2. Fic. 7. USNM 131671; external view of a large left valve. Compare ornament with that of fig. 3. Locality data as above. x 2. = LS 1967 REVISION OF SYNCYCLONEMA 19 but only one crus on the posterior auricle of the left valve, whereas Syncyclonema has one crus on each auricle. The outer ends of the ventral crura on Eburneopecten bend upwards to meet the dorsal crura below the dorsal extremities of the auricle thus defining a cuneiform-shaped area (pl. 4, figs. 4, 5). Those on the left valve probably fit inside those of the right valve which are stronger. The dorsal crura and sockets of Eburneopecten adjacent to the resilifer are transversely striated (pl. 4, fig. 5). The tooth- like processes on either side of the resilifer on the right valve are short and weak on Eburneopecten (pl. 4, fig. 4), but long and strong on Syncyclonema (pl. 3, fig. 2). Eburneopecten has dis- tinct incipient auricular crura which are stronger on the left valve. The shape and position of the adductor muscle impression are different. The scar of Eburneopecten is larger and situated more centrally (pl. 4, fig. 5) than that of Syncyclonema which is close to the base of the posterior ear. These internal morphological differences are sufficient to show there is no close relationship between Syncyclonema and Eburneopecten. 3. GENUS MICRONECTES AUTHOR. Ichikawa & Maeda, 1958, p. 95. TYPE SPECIES. By original designation, Micronectes bellaturus Ichikawa & Maeda (1958, p. 98, pl. 5, figs. 13-17; see pl. 5, figs. 1-9 herein), Late Cretaceous (Campanian-Maastrichtian), Japan. COMPARISON WITH SYNCYCLONEMA. Micronectes differs con- siderably from Syncyclonema in external and internal morphology. The strongly inflated valves of M. bellaturus have a distinctive ornament of non-punctate, flat- and round-topped radial costae and strong concentric lamellae (pl. 5, figs. 2, 6, 9). The costae become flat-topped on the ventral part of the shell and are three or four times wider than the narrow depressions which, together with the corrugation of the edge of the lamellae and a pseudo- punctate effect produced by the intersection of the lamellae and radial grooves, become the dominant features. This ornament resembles that of species placed by Grau (1959) in Cyclopecten 20 Postilla YALE PEABODY MUSEUM No. 110 (s.s.) and C. (Delectopecten), but is quite different from the fine submacroscopic radial markings on the compressed valves of Syncyclonema halli. The anterior auricle of the right valve of bellaturus bears four to six radial costae above a very wide fasciole, the byssal notch is deep and wide, and contrary to Ichikawa & Maeda’s statement, there is a strong ctenolium (pl. Dey By these characters Micronectes closely resembles Campto- nectes, but not Syncyclonema. Each auricle has a strong cardinal crus. That on the left valve is separated by a narrow but deep socket from a prominent flat-surfaced crus extending the length of the dorsal margin (pl. 5, fig. 3). The resilifer of the right valve is deeply sunken and appears to lack bordering tooth-like proc- esses. In contrast, Syncyclonema lacks the dorsal flat-surfaced crus and has tooth-like processes adjacent to the resilifer. 4. GENUS PECTINELLA AUTHOR. Verrill, 1897, p. 68. TYPE SPECIES. By original designation, Pecten sigsbeei Dall (1886, p. 223, pl. 4, fig. 2), from “off Havana”, Cuba, Recent. DISCUSSION. Verrill (1897, p. 68) gave the following generic diagnosis. “Shell small, thin, swollen, nearly smooth, with convex and slightly unequal valves. Auricles very unequal, oblique, the ante- rior larger, with a deep byssal notch in the right valve, but with- out pectinidial teeth; posterior auricle small. The surface is smooth except for fine lines of growth. Camptonectes sculpture is not present. The texture is not hyaline.” Verrill based his diagnosis of the genus on P. sigsbeei, the only species he included in his new taxon. As the diagnosis is inadequate for present day systematics, and is also erroneous, the opportunity is taken to redescribe the type species. An emended diagnosis is not given as it should await a review of species included in the genus and other closely related taxa. The redescription of the type species was facilitated by Dr. W. J. Clench, Museum of Comparative Zoology, who kindly 1967 REVISION OF SYNCYCLONEMA Da sent me data and photographs of a right valve (MCZ 7817; pl. 6, figs. 1, 4) of sigsbeei, labeled as holotype, from “off Havana”, and by Dr. J. Rosewater, U.S. National Museum, who kindly sent me a left valve (USNM 62263; pl. 6, figs. 2, 3) of P. sigsbeei Dall, from “Depth 158 fms., Lat. 22°10/N, long. 82°20’W, U.S. Coast Survey, C. P. Patterson, supt., Gulf Stream and Gulf Mexico Explor., USCG., S. Blake, Alex Agassiz, 1877-78”, and labeled “type fig’d.” Dr. Rosewater also sent a larger left valve (pl. 6, figs. 5-7) USNM 503313, from “off English Harbor, Antigua, 120 fms, rough coral.” Pectinella sigsbeei (Dall) (PIG, hes. 1-7) Pecten (Pseudamussium) sigsbeei Dall, 1886, p. 223, pl. 4, fig. 2. Pectinella sigsbeei (Dall). Verrill, 1897, p. 68. TYPE SPECIMENS. Holotype by original designation MCZ 7817, a right valve from near Havana, Cuba, Lat. 22°10’W, Long. 82°20’, 158 fathoms, Recent, and the probably matching left valve USNM 62263 from the same locality. Several lines of evidence indicate that the left (USNM 62263) and right (MCZ 7817) valves originally came from the one bivalved specimen, and together should be treated as the holotype, especially as these were the only valves available to Dall at the time he described the species. 1. Measurements made on the three valves are as follows: MCZ 7817 USNM 62263 USNM 503313 (right valve ) (left valve ) (left valve ) Length or mi 9.4 Bias) Height Qs) 10.5 16.2 Half width — 7 322 Length of dorsal margin 4.3 4.2 eS Anterior length of dorsal margin Pigs) 2.8) c. 4.4 (incomplete ) i) i) Postilla YALE PEABODY MUSEUM No. 110 Even though the measurements of MCZ 7817 are taken from a negative, the coincidence of the measurements of the right valve MCZ 7817 and the left valve USNM 62263 is noteworthy and suggests that the two valves are from one bivalved specimen. 2. The presence of dried body tissue and ligament adhering to the inner surface of the left valve USNM 62263 (this tissue was later removed to improve the specimen for photography) and the apparent presence of similar material on the hinge area of the right valve MCZ 7817. 3. The data on the label accompanying USNM 62263 matches that given by Dall (1886, p. 223) in his original description of the species. 4. Dall recorded “two valves were obtained by Sigsbee”’, and his description shows he had a left and a right valve. The right valve (MCZ 7817) clearly matches Dall’s figure (1886, pl. 4, fig. 2), but to my knowledge, and contrary to the label (see above) the left valve (USNM 62263) has not been figured pre- viously (pl. 6, figs. 1-4). 5. The extremity of the anterior auricle of both the left and right valve is incomplete, suggesting the possibility of breakage when conjoined. Although Dall (1886, p. 175) notes that the “types of species described will be found in the Museum of Comparative Zoology at Cambridge, and in the U.S. National Museum” it is most unusual that a collection should have been split into two parts. However, in the case of P. sigsbeei one valve seems to have been lodged in each institution. Dall, in his original description, did not select a specific speci- men as the holotype. But because the label accompanying the right valve MCZ 7817 is marked as holotype, apparently in Dall’s handwriting, and as Dall, in the sentence quoted in the previous paragraph, mentions depositing types in two institutions, the desig- nation of the holotype is taken as being by original designation. REVISED DESCRIPTION. Small, shell thin, equivalve, inequilateral, strongly inflated. Umbones small, project only slightly above the dorsal margin. Antero-dorsal margin of the right auricle projects dorsally and overlaps the margin of the left valve. Auricles of 1967 REVISION OF SYNCYCLONEMA 23 the left valve and posterior auricle of right valve not sharply delimited from disc of valve; anterior auricle of right valve with a very narrow fasciole. Anterior auricles much larger than the posterior. Right valve with a deep open V-shaped byssal notch; no ctenolium. Auricles ornamented with fine raised concentric costae, 11-13 per millimeter, and much finer submacroscopic radial costae which cross only the interspaces between the concentric costae. Disc of shell appears smooth except for occasional growth lines and pauses; but has submacroscopic, very fine, regular, raised concentric striae, about three per 0.1 mm over entire surface of shell. Disc crossed by faint submacroscopic radiating sulci which are im- pressed only in the interspaces between the raised concentric striae and give the shell a fine pseudo-punctate appearance. Radial sulci diverge and are more distinct on the dorsal flanks of the disc. Radial sulci about one-fourth to one-sixth of the width of the flat-crested interspaces, and about four to six per 0.1 mm. Left valve with a flat, longitudinally finely striated ligament surface just below the dorsal margin of each valve. Below the flat surface on the anterior auricle is a narrow linear socket followed by a long, strong cardinal crus. Posterior ear similar, with a cuneiform-shaped depression defined ventrally by a cardinal crus which is strongest near the resilifer and at its posterior end, and which extends postero-ventrally and then bends up sharply to meet the end of the flat surface. Right valve with a strong cardinal crus on each auricle. These fit into matching depressions above the crura of the left valve. The presence of flat ligament surfaces on the right valve is uncertain, but probable, judging from the photograph (pl. 6, fig. 4). Base of each auricle has a nodular auricular crura, with the posterior being the stronger. Resilifer small, with on the left valve two shallow depressions on either side. These suggest the presence of short, weak tooth-like processes on either side of the resilifer of the right valve. Musculation and shell structure unknown. DISCUSSION. Both left valves are similar except for stronger car- dinal crura and more distinct radial ornament on the umbone of USNM 62263. 24 Postilla YALE PEABODY MUSEUM No. 110 COMPARISONS. Pectinella sigsbeei is externally similar to Syncyclo- nema halli. The main differences are in the details of ornament, the strong inflation of the valves, and the very small posterior auricle of P. sigsbeei. Both species have similar concentric lamellae on the auricles, but the radial ornament of S. halli is much stronger than that of P. sigsbeei and its concentric striae are not so regular or distinctive. Consequently, S. halli does not have the pseudopunctate effect of P. sigsbeei. S. halli lacks the strong auricular crura of P. sigsbeei, and has strong tooth-like processes on either side of the resilifer against possibly only weak ones on P. sigsbeei. The auricles of the left valve of P. sigsbeei have dorsal flat ligament bearing areas which are lacking on S. halli. The cardinal crus on the posterior auricle of the left valve of P. sigsbeei is arcuate and concave upwards (pl. 6, fig. 6), that of S. halli is straight (pl. 3, fig. 1). The cardinal crus on the ante- rior auricle of the left valve of P. sigsbeei is long and strong (pl. 6, fig. 5) whereas that of S. halli is weaker, sometimes discon- tinuous, though relatively strong close to the resilifer and _ its anterior end where the swollen part is displaced dorsally relative topthe rest of (the crus (pli 3. fies; >). These morphological differences are sufficient to warrant accepting Syncyclonema and Pectinella as distinct genera. A knowledge of the musculation might give additional support to my conclusion. Hayami (1965, p. 318) reclassified a Japanese Lower Cre- taceous species, Pecten miyakoensis Nagao, under Pectinella. Study of casts of P. miyakoensis (NZGS-WM 8473) shows that externally the species resembles both S. halli and P. sigsbeei. But the strongly projecting dorsal extremities of the auricles of the right valve of P. miyakoensis are not matched by either species. P. miyakoensis more closely resembles S. alli in the strength and form of the radial and concentric ornament and lack of a pseudo- punctate effect. As recognized by Hayami the ornament of P. miyakoensis tends to be discrepant with stronger concentrics on the right valve and stronger radials on the left valve. Also the ornament of P. miyakoensis is markedly finer, and the radial ornament more restricted to the dorsal flanks of the disc. P. miyakoensis, like S. halli, lacks auricular crura. Contrary to Hayami’s (1965) description, a right valve of P. miyakoensis 1967 REVISION OF SYNCYCLONEMA 25 has cardinal crura. (These are faintly visible on pl. 45, fig. 6, of Hayami, 1965, Gk H6622). On either side of the sunken resilifer, flat longitudinally striaed surfaces pass laterally into narrow crura which extend halfway to the extremities of the auricles. Small rounded protuberances extend ventrally from the triangular surfaces on either side of the resilifer. The form and arrangement of the crura and the strongly projecting auricles of the right valve distinguish P. miyakoensis from both Syncyclonema and Pectinella, and the lack of tooth-like processes on either side of the resilifer distinguishes it from Syncyclonema. Future studies on small, relatively smooth pectinids may war- rant placement of P. miyakoensis in a separate supra-specific taxon. Until adequate studies are completed, it is best to treat it as a Pecten (sensu lato). Except for the large byssal auricle and notch P. miyakoensis superficially resembles species of Ento- lium by its possession of strongly projecting dorsal margins and short cardinal crura. 5. GENUS HYALOPECTEN AUTHOR. Verrill, 1897, p. 71. TYPE SPECIES. By original designation, Pecten undatus Verrill & Smith, in Verrill, 1885, p. 444, pl. 44, fig. 21 (= Hyalopecten dilectus Verrill & Bush, in Verrill, 1897, p. 80, pl. 18, fig. 5; see North, 1951), North-west Atlantic Ocean, Recent. DISCUSSION. To document the differences between Syncyclonema and Hyalopecten the poorly known type species of the latter is redescribed from its holotype. Grau (1959) classes Hyalopecten as a subgenus of Cyclopecten Verrill (1897). Hyalopecten dilectus Verrill & Bush (CELSO. tiess