Abrachlamys 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, figs. 1-67. [p. 38]
«Genus Abrachlamys gen. nov.
Type species. Abrachlamys toolinnensis sp. nov., Early Miocene, Eucla Basin, Western Australia.
Diagnosis. Chlamydini of rather wide, short, aequipectinoid shape, retaining a deep, narrow byssal notch and chlamydoid RV anterior auricle in adults; valves about equally inflated; radial sculpture of almost fixed number of undivided costae, few costal subdivisions seen on some specimens; with antimarginal ridgelets over all intercostal surfaces, and on disc margins and auricles; radial costae and auricles of LV bearing numerous, regularly and widely spaced, low commarginal lamellae, about 1 mm apart in centre of disc, raised into low scales on costal crests, weakly continuous across radial interspaces; on RV, identical lamellae to those of LV present only on auricles and on few, narrower, more closely spaced costae on anterior and posterior ends of disc, costae on most of RV disc smooth apart from antimarginal ridgelets; internal expressions of external costae are merely corrugations, without internal rib carinae. One low, narrow intermediate tooth on each side of hinge in one RV; not seen on other material. LV preradial sculpture not known.
Remarks. The new genus is proposed for a single species that does not fit well into any genus of Pectinidae with which we are familiar. Clearly chlamydinine characters displayed by Abrachlamys toolinnensis gen. nov., sp. nov. are the lack of internal rib carinae (although that could occur in primitive members of almost any tribe), the presence of dominant antimarginal ridgelets over all the shell surface and the retention of the chlamydoid deep byssal notch and ctenolium in the adult. The rather wide, aequipectinoid shape is unusual for a member of the Chlamydini, but is seen in some other undoubted members such as Serripecten, Equichlamys, and Talochlamys species of the T. keiloriana species group (including the Abrakurrie Limestone species T. multilamellata). The commarginal lamellae might be taken for those of the Palliolini, were it not that they are absent over most of the RV, and are spaced about 1 mm apart over the central area of the LV disc, much more widely apart than the normal microsculpture of Palliolini. The little-divided radial costae also are an unusual character for a member of the Chlamydini, and the presence of what appear to be intermediate hinge teeth in one specimen is an anomalous character for the Chlamydini. The lack of knowledge of most other phylogenetically useful characters makes it difficult to assess the relationships of Abrachlamys, particularly not knowing the LV preradial microsculpture, but the balance of characters and, in particular, the persistent antimarginal ridgelets, indicate a position in Chlamydini. Dr T. R. Waller has pointed out (1999, pers. comm.) that many species of Eocene and Oligocene age from Europe and the eastern USA are very similar to Abrachlamys toolinnensis gen. nov., sp. nov. in many characters—in their broad shape, with umbonal angles greater than 90°, in their deep byssal notch, in their relatively simple costae that show only a slight tendency to increase in number during ontogeny, in their low convexity, in their costate disc flanks, in their commarginal lamellae lacking the ventrally convex intercostal flexure of the Aequipecten pattern, and in lacking internal rib carinae. It appears likely, then, that species related to Abrachlamys, and possibly congeneric with it, are widespread in Paleogene rocks. However, study of and comparison with these extra-Australian species is beyond the scope of this revision.
A possible second Australian species of Abrachlamys seems to be represented by specimens illustrated by Ludbrook (in Lowry 1970: fig. 21A, E) under the names ‘Chlamys cf. sturtianus’ [sic] and ‘Chlamys eyrei’. These specimens are from ‘Toolinna Limestone’ (a local facies of the Eocene Wilson Bluff Limestone or possibly Abrukurrie Limestone according to Li et al. 1996) at Toolinna Cove, Great Australian Bight, and are housed by GSWA. More material is needed before this taxon can be evaluated. Etymology. The generic name (Abrakurrie + Chlamys) refers to the formation, Abrakurrie Limestone, that was the provenance of the type species. Gender feminine.»
ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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Abrachlamys toolinnensis sp. nov., type species of Abrachlamys gen. nov.; A. G. Beu & T. A. Darragh, 2001, Revision of southern Australian Cenozoic fossil Pectinidae, figures 8A, 8C-8E.
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