Veprichlamys leprosa Beu & Darragh, 2001
BEU, A. G. & T. A. DARRAGH. 2001. Revision of southern Australian Cenozoic fossil Pectinidae (Mollusca: Bivalvia). Proceedings of the Royal Society of Victoria, 113: 1-205. [p. 115, figs. 39D-F, 40A-H]
2001 Veprichlamys leprosa Beu & Darragh, 2001
A. G. Beu & T. A. Darragh, 2001, figures 39, 40.
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«Description. Small for genus (to c. 20 mm high), relatively short and wide, ie., with wide umbonal angle for genus (c. 97-100º); height only slightly greater than length, very weakly inflated, the two valves about equally inflated, shape weakly to moderately prosocline. LV preradial dissoconch sculptured with prominent, narrow, closely spaced antimarginal ridgelets, crossed by narrow, strongly elevated, widely spaced commarginal ridges, forming commarginal zones of short ridgelets. Disc sculpture of c. 36-50 narrow, well raised, convexcrested radial costae, increasing irregularly in number down disc, so interspaces remain constant in width on many specimens but increase markedly in width down disc on others; secondary and tertiary costae added by intercalation in centre of interspaces on RV, by both subdivision and a lesser degree of intercalation on LV; all costae bearing many narrow, short to moderately long, ventrally cupped, ventrally directed spines. Radial interspaces closely sculptured with antimarginal ridgelets, some in centre of disc remaining straight and continuous for most or all of disc height. Anterior auricles long; on RV with deep byssal notch, functional ctenolium, wide, deeply sunken byssal fasciole bearing many prominent commarginal ridges, and main face above byssal fasciole sculptured with 4-5 prominent radial costae crossed by very prominent, irregular commarginal lamellae that serrate dorsal margins; on LV tall, with anteriorly sloping, weakly sinuous anterior margin, strongly pointed at anterodorsal extremity, sculptured with 6-9 prominent radial costae as on disc, bearing more prominent spines than on disc. Posterior auricles short, with strongly concave posterior margins, strongly pointed at posterodorsal extremity, sculptured with only 2-4 very narrow, widely spaced radial costae. Interior smooth apart from very weakly sinuous ventral margin. Hinge with long, very narrow dorsal teeth and very short, extremely narrow resilial teeth.
Type material. Holotype, NMV P302793, figured paratype, NMV P302794, one paratype, NMV P302795, and 21 other specimens, Fyansford Formation (Baimsdalian), ‘middle beds’ at Grice’s Creek, Mount Eliza, 8 km south of Frankston, Victoria, coll. F. A. Cudmore, 1940; NMV P302796-7, 2 paratypes and NMV P301357, c. 50 other specimens, Grice’s Creek, Mount Eliza, 8 km south of Frankston, Victoria, coll. F. A. Cudmore, 1905.
Other material examined. Balcombian: FYANSFORD FORMATION: Orphanage Hill road cutting, Fyansford (5 specimens); PL3077, Altona Bay coal shaft (5 specimens). Baimsdalian: FYANSFORD FORMATION: PL3104, Manyung Rocks (2 specimens); Grice’s Creek (2 specimens). Occurrence and time range. Balcombian and Baimsdalian; limited to Fyansford Formation in the Melbourne district. Remarks. In most characters, Veprichlamys leprosa sp. nov. is a typical species of Veprichlamys, the only one we know of occurring fossil in either Australia or New Zealand. It differs from V. perillustris in many obvious characters, particularly the much smaller size (V. perillustris reaches at least 38 mm in height), the much shorter and wider, less markedly prosocline disc, and the more numerous, more crowded, more frequently subdivided and intercalated radial costae, bearing more numerous spiny scales than in V. perillustris. The LV preradial dissoconch sculpture also is markedly more prominent than in V. perillustris; although very similar in the spacing of the commarginal ridges and antimarginal ridgelets, the preradial sculpture of V. perillustris is much more subdued, and gives the appearance of having been smoothly abraded off. A similar evolutionary series from a more coarsely sculptured LV preradial dissoconch in Miocene species to weaker sculpture in younger species is seen also in Semipallium, Talochlamys and Mimachlamys, indicating that a reduction in the prominence of the earliest sculpture on the LV is a common evolutionary trend in the Pectinidae. Although the antimarginal ridgelets on the central few radial interspaces of the disc of V. leprosa are unusually straight and continuous, none is quite as prominent and strictly continuous as in V. perillustris (Fig. 39H). The New Zealand Recent species Veprichlamys kiwaensis (Powell) (1933: 371, pl. 40, figs 1-5) was originally collected from a cable hauled up from ‘between 600 and 700 fathoms) [c. 1025-1280 m], about 650 km west of New Plymouth, ie., presumably on the Challenger Plateau. This species has since proved to be quite common around New Zealand in moderate depths, and many lots in the Museum of New Zealand Te Papa Tongarewa were compared with V. perillustris and V. leprosa sp. nov. In general appearance V. kiwaensis is more similar to V. perillustris than V. leprosa, as like V. perillustris it consistently has very narrow, widely spaced, prominent radial costae with long, narrow, semitubular, ventrally directed spines on the costal crests, and with only minor bifurcation and intercalation of secondary costae, rather than having the many, fine closely spaced, secondary radial costae that are present on V. leprosa. V. kiwaensis reaches a slightly smaller maximum size, is much less strongly prosocline, is slightly more inflated, and has a significantly shorter RV anterior auricle and a shorter, much taller and straighter anterior margin to the LV anterior auricle than in V. perillustris. In most characters, then, V. leprosa sp. nov. actually is nearer to V. kiwaensis than V. perillustris, differing from V. kiwaensis in its smaller size, its still less markedly prosocline shape, its longer and more sinuous anterior margin to the LV anterior auricle, and its much more numerous secondary radial costae. The sculpture of the LV preradial dissoconch of V. kiwaensis has the same prominent, sharp commarginal ridges crossing relatively prominent antimarginal ridgelets as occurs in V. perillustris (Fig. 39D, F), and the antimarginal ridgelets in the costal interspaces over the central part of the disc of V. kiwaensis are long, parallel and straight as in V. perillustris. In its longer and wider shape, its much less strongly prosocline disc, its longer posterior auricles and its taller but more weakly sinuous-margined LV anterior auricle, the adult of V. leprosa resembles the juvenile stage of V. perillustris. This suggests the possibility that V. perillustris (and possibly also V. kiwaensis) evolved from V. leprosa by a heterochronic process (McKinney & McNamara 1991). As far as we are aware, this is the first published record of a pre-Pliocene species assigned to Veprichlamys. Etymology. The specific name (Latin, ‘leprosus’, literally leprous, or scaly) refers to the fine scaly sculpture of this species.» ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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