Serripecten excultatus 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. 79, fig. 23A-C]
2001 Serripecten excultatus Beu & Darragh, 2001
«Description. Shell of moderate size for genus (to c .70 mm high), polished and weakly sculptured, with inflation of both valves about equal. Umbonal angle 120-130°, increasing in larger specimens. RV polished, sculptured only with very faint radial striations over proximal third of disc, sculpture strengthening over central third of disc, until by distal third of disc of large specimens sculpture consists of c. 100-110 very low radial costae, with interspaces equal to or slightly wider than one costa, of symmetrical section and smooth-crested over most of disc, slightly more prominent, narrowcrested and inclined towards anterior near anterior end and towards posterior near posterior end, weakly and irregularly subdivided and intercalated to increase in number across disc, bearing very low, weak, closely spaced commarginal scales near ventral margin of some large specimens. LV similar to RV in being weakly sculptured over proximal third, developing weak but regularly increasing, obscure, smooth radial ridges over central third of disc, and sculptured with c. 110 low, wide, obscurely margined, closely spaced radial costellae over distal third of disc, differing from RV in having normal low, widely spaced commarginal lamellae of Serripecten over entire surface of distal half of disc. Posterior auricles of both valves significantly taller than anterior ones, with posterior margin nearly straight, inclined strongly towards anterior; RV anterior auricle with deep byssal notch, deeply depressed, narrow byssal fasciole and functional ctenolium in all specimens seen (ie., adults evidently byssally attached); RV auricle dorsal margins closely and finely serrate; LV anterior auricle with only very weakly sinuous, nearly vertical anterior margin; all auricles sculptured as on neighbouring disc. Interior without rib carinae. Hinge with low, narrow, but obvious dorsal and resilial teeth.
Dimensions.
Holotype, P302072 H 63.2 L 66.3 RV Paratype, P302073, Browns Creek 61.8 63.1 RV Paratype, P302074, Browns Creek 54.2 57.2 LV Type material. Holotype, NMV P302072, Browns Creek Clay (Aldingan), PL3014, above dark gritty clay, at top of section in gully nearest mouth of Johanna River, Browns Creek, Johanna district, Victoria, grid ref. Glen Aire 079058; coll. T. A. Darragh, 12.xi.I984; 2 paratypes (one RV, one LV), NMV P302703^t, all data as holotype.
Other material examined. Aldingan: BROWNS CREEK CLAT: PL3014, type locality (9 specimens); PL3016, Castle Cove (14 specimens); WAM 94.618, type locality (32 specimens); AMS C135207, Castle Cove (2 specimens). Occurrence and time range. Late Aldingan (late Eocene); restricted to the top of Browns Creek Clay at Browns Creek and the nearby Castle Cove, southern Victoria.
Remarks. S. excultatus sp. nov. differs from almost all the other Australian species of Serripecten by having very weak sculpture, with the proximal half of the disc of both valves polished and almost smooth, and sculpture developing gradually out across the rest of the disc. The sculpture on the anterior and posterior ends of the RV and on the distal part of the LV is similar to that of adult specimens of S. aldingensis but, as S. aldingensis is much smaller than S. excultatus, this shows that the sculpture of S. excultatus is much the finer. All other species have markedly coarser sculpture. S. excultatus superficially resembles the New Zealand Oligocene and Late Eocene species assigned to Janupecten Marwick, 1928 (ie., the real Lentipecten) and, although the RV sculpture of S. excultatus is similar to that of some 'Janupecten’ species, these all have an almost smooth LV, with only faint radial ridgelets developing near the ventral margin on a few specimens, and all lack the scaly, fine, closely spaced radial costellae of the LV of Serripecten. Etymology. The specific name (Latin, ‘excultus’, polished) refers to the external surface of the valves.» ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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