Serripecten carteri 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. 93, figs. 28A, B]
2001 Serripecten carteri Beu & Darragh, 2001
A. G. Beu & T. A. Darragh, 2001, figure 2.
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«Description. Very large (to c. 150 mm high and 180 mm long), larger specimens markedly longer than high, smaller ones less obviously so; RV significantly more inflated than LV. Umbonal angle extremely wide (to 145-150° in large specimens); angle of posterior margin below hinge line significantly greater than anterior angle, ie., posterior auricle a little taller than anterior auricle. RV disc sculptured with c. 46-52 primary radial costae, similar to bevelled costae of S. yahliensis in general appearance (ie., with steep face towards anterior or posterior ends of shell, gentle slope towards centre of disc) but gentle slope towards centre more concave, producing a wide, almost flat intercostal space that bears 3-6 low, narrow, sharply defined costellae, with central costella raised into a narrow, well defined median costa in some interspaces; serrate scaly sculpture of steep anterior faces of anterior costae and posterior faces of posterior costae much finer and less obvious than in S. yahliensis. LV disc sculptured with c. 85-120 low, narrow radial costae, more clearly defined than on RV, with several fine secondary and tertiary costellae in interspaces, all crossed by numerous low, thin, closely spaced commarginal lamellae that form low scales on costal crests. Auricles extremely long and low, hinge length up to 60% of disc length (auricles 100 mm long on disc 168 mm long in holotype), anterior auricle of large specimens with very shallow remnant of byssal notch in RV and shallowly sinusoidal anterior margin in LV, posterior margin of both posterior auricles nearly vertical, lightly convex in outline; RV auricles separated from disc by shallow groove only, byssal fasciole of anterior auricle raised above neighbouring disc surface; LV auricles separated from disc by moderately deep, wide groove in small to moderately large specimens, becoming shallower with growth to form only moderately shallow groove in large shells. Ctenolium not functional in adult, remaining as a clearly visible row of teeth in groove between auricle and disc for about half shell height, or slightly greater, to point where byssal notch shallows markedly. Posterior auricles of both valves and LV anterior auricle sculptured as on neighbouring disc, RV anterior auricle very weakly sculptured, with low radial costae proximally but little sculpture distally. Dorsal margins of RV auricles finely and closely to moderately coarsely serrate. Interior surface smooth. Hinge with very long, narrow, prominent dorsal teeth and sockets, but low, rather inconspicuous resilial teeth and sockets.
Dimensions.
Holotype, P300116 H 142.8 L 167.9 RV Paratype, P302214, PL3267 134.1 150.7 RV Paratype, P302215, PL3267 116.9 127.1 RV Paratype, P300122, PL3110 130.6 146.9 LV Type material. Holotype, NMV P300I16, Tambo River Formation (Mitchellian), PL3110, road cutting on Swan Reach-Metung Road, left bank of Tambo River, 200 m south of Princes Highway, Swan Reach, Lakes Entrance, Gippsland, Victoria, grid ref. Bairnsdale 759132, coll. F. A. Cudmore, 1939; paratype, NMV P300I22, same data as holotype, don. University of Melbourne, 1989; 2 paratypes, NMV P302214-5, Tambo River Formation (Mitchellian), PL3267, low outcrop on shore of Reedy Arm peninsula, Nowa Nowa Arm, Lake Tyers, Lakes Entrance, Gippsland, grid ref. Orbost 994159, coll. A. N. Carter.
Other material examined. Mitchellian: TAMBO RIVER FORMATION: PL3110, Swan Reach cutting (9 specimens); PL3267, Reedy Arm peninsula, Lake Tyers (33 specimens); Nowa Nowa Arm, Lake Tyers (1 specimen). Cheltenhamian: BLACK ROCK SANDSTONE: Beaumaris (9 specimens); Cheltenham (3 specimens) (all referred tentatively). Occurrence and time range. Apparently restricted to Tambo River Formation in the Gippsland Basin; uncommon at the type locality and abundant in the low outcrop on the Nowa Nowa Arm, Lake Tyers. The few large Serripecten specimens (ie., as distinct from S. semilaevis) from Beaumaris, near Melbourne (type Cheltenhamian) are too poorly preserved to determine whether they are S. carteri or S. yahliensis, although it seems likely that they are S. carteri, and we refer them there tentatively. It appears likely that S. carteri sp. nov. is a Mitchellian (and presumably Cheltenhamian) descendent of S. yahliensis, and it may have some utility in Gippsland biostratigraphy. Remarks. Serripecten carteri sp. nov. reaches an even larger size than its apparent immediate ancestor, S. yahliensis, and is very similar to it in shape and in general appearance. It differs from S. yahliensis in almost losing the byssal notch in large specimens, with only a shallow sinus remaining, in having the auricles almost completely fused with the disc surface on the RV and separated by only a shallow groove on the LV, so that the slightly swollen byssal fasciole of large specimens protrudes above the disc surface (in strong contrast to the deep, undercut grooves demarcating the auricles in S. yahliensis) and, most obviously, in having wider and more obvious radial interspaces that bear numerous fine secondary and tertiary costellae that are not present, or are represented by only an occasional single thread in most interspaces and several in a few interspaces, in S. yahliensis. The serrate sculpture and serrate dorsal margin are also much less prominent on S. carteri than on S. yahliensis. As with S. squamocostatus sp. nov., the LV is little different from that of S. yahliensis, except for its shallower grooves between the disc and the auricles, and we have not felt it necessary to illustrate the LVs of these species. The new species cannot be confused with any other species of Serripecten, all of which are much smaller. Etymology. We have great pleasure in naming the new species in honour of the late Alan N. Carter, formerly of the University of New South Wales and the Geological Survey of Victoria, to record his long interest in the stratigraphy and foraminiferal biostratigraphy of Gippsland, as well as his great interest in scallops (eg., see Carter 1966). Alan was the first to collect at many of the localities we report here around Lake Tyers (see under Mesopeplum meringae), including the locality with common Serripecten carteri, and we have utilised his collections (now in NMV) in this work. ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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