Serripecten squamocostatus 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. 82, figs. 23D-F]
2001 Serripecten squamocostatus Beu & Darragh, 2001
«Description. Moderate-sized for genus (to c. 70 mm high), RV moderately inflated, LV more weakly inflated than RV, length slightly to moderately greater than height; umbonal angle very wide, 130-140°; the most coarsely sculptured of Australian Serripecten species. RV sculptured with c. 33-37 relatively wide, moderately high primary radial costae of almost symmetrical, rounded section, narrower than on centre of disc and inclined slightly towards anterior near anterior end, narrower and inclined slightly towards posterior near posterior end, with interspaces each about twice width of one costa, bearing at least one narrow secondary costa in centre of each interspace, interspaces wider and bearing a few, irregular tertiary costellae on posterior fifth of disc of most specimens and on anterior fifth of some specimens; all crossed by low, regular, evenly spaced commarginal lamellae, up to c. 1 mm apart over centre of disc of large specimens, closer near anterior and posterior ends and towards ventral margin of large specimens, forming very low scales on costae. LV sculpture of c. 55-60 low, wide, primary radial costae, with interspaces about equal to or slightly wider than one costa, each interspace with one low, wide, central secondary costa arising early on disc and, in many specimens, rivalling or equalling primary costae in prominence by ventral margin; all crossed by thin, continuous, wavy commarginal lamellae, varying from slightly higher than on RV, forming low ventrally concave scales on costae, to 3-4 times height of RV lamellae, and thickened and elevated still further on costal crests to form thick, prominent, rather widely spaced, ventrally curved scales. RV anterior auricle with moderately deep, rather narrow byssal notch and weakly elevated byssal fasciole, ctenolial teeth present in narrow, shallow groove between auricle and disc on some specimens but apparently not functional in large specimens; byssal fasciole slightly raised above surface of neighbouring disc; flat upper area of auricle, above byssal fasciole, sculptured with 4-6 radial costae, as on disc, crossed by close, high, coarse commarginal lamellae; RV posterior auricle taller than anterior one, with strongly convex posterior margin, sculptured with narrow radial costae and thin lamellae as on neighbouring disc, separated from disc by moderately deep, undercut groove. LV anterior auricle moderately short, sculptured as on neighbouring disc, with anterior margin sloping slightly towards posterior, separated from disc by moderately deep, undercut groove; LV posterior auricle taller than anterior one, sculptured as on neighbouring disc, separated from disc by undercut groove as at anterior. Dorsal margins of RV auricles strongly but narrowly and sharply serrate. Interior smooth. Hinge with low, narrow but obvious dorsal teeth and short, low, obscure resilial teeth.
Dimensions.
Holotype, P302082, PL3191 H 59.8 L 65.4 RV Paratype, P302085, PL3231 63.9 68.4 RV Paratype, P302083, PL3196 66.1 70.8 LV Paratype, P302081, PL3191 47.2 47.6 LV Type material. Holotype, NMV P302082, Mannum Formation (Longfordian), PL3191, cutting on Klose Road, c. 400 m N of junction with Manrium-Purnong Road, 6 km NE of Mannum, South Australia, grid ref. Mannum 499395, coll. A. G. Beu & T. A. Darragh, 20.ix.1993; paratype, NMV P302081, all data as holotype; paratype, NMV P302083, Mannum Formation (Longfordian), PL3196, cliff at N end Big Bend Reserve, left bank Murray River, 7 km NNW of Nildottie, South Australia, grid ref. Swan Reach 727670, coll. A. G. Beu & T. A. Darragh, 22.ix.1993; paratype, NMV P302085, Gambier Limestone (here Longfordian), PL3231, quarry N of Donovans Road, c. 1 km SW of ‘Summer Hill’, 2.6km west of Donovans, South Australia, grid ref. Gambier 937929, coll. A. G. Beu & T. A. Darragh, 9.xi,1993; NMV P302084, paratype, Gippsland Limestone (Longfordian), PL3251, Merrimans Creek quarry, nr Stradbroke West, Gippsland, grid ref. Stradbroke West 952652, coll. A. G. Beu & T. A. Darragh, 17.xi.1993.
Other material examined. Longfordian: MELTON LIMESTONE: PL3295, Myponie P t (2 specimens); GAMBIER LIMESTONE: PL3231, quarry off Donovans Rd (4 specimens); GIPPSLAND LIMESTONE: PL3251, Merrimans Creek quarry (4 specimens); MANNUM FORMATION: PL3181, cutting near Reedy Creek (1 specimen); PL3186, cutting opposite Kia Marina (10 specimens); PL3191, cutting, Klose Rd, Mannum (13 specimens); PL3194, Walker Flat (3 specimens); PL3196, Big Bend Reserve (2 specimens); PL3212, Murray cliffs, ‘Cave Cliff’ (1 specimen); lower beds, Murray River cliffs, Overland Corner (1 specimen); Murray cliffs opposite centre of entrance to lagoon, Punyelroo (3 specimens); lower beds, Murray cliffs, Wongulla (6 specimens); lower beds, Murray cliffs, Wongulla to Mannum (8 specimens); Murray River cliffs, Nildottie (1 specimen); WAM 86.356, cliff E side Murray River, Ponde Rd, 1.9 km from turnoff from Mannum -Murray Bridge Rd (1 specimen). Occurrence and time range. Apparently restricted to Longfordian. We have seen specimens only from Mannum Formation along the Murray River, from Gambier Limestone around Mount Gambier (where it is much less common than S. yahliensis), and from Gippsland Limestone at Merrimans Creek, near Stradbroke, Gippsland.
Remarks. Serripecten squamocostatus sp. nov. is similar in size to S. excultatus sp. nov., differing in having a much thicker shell and very much coarser sculpture. It is usually much smaller and, for its size, more coarsely sculptured than S. yahliensis, although specimens from Gambier Limestone are no smaller than the largest specimens of S. yahliensis from there. The more prominent, more widely spaced radial costae of narrower, rounded rather than wide, bevelled, narrowly crested section, without triangular scales, and with one to several consistent secondary and tertiary costellae, and the more prominent, more continuous commarginal lamellae distinguish the RV sculpture readily from that of S. yahliensis, and the wider, less numerous costae and much coarser scales distinguishes the LV from that of S. yahliensis. In fact, S. squamocostatus much more nearly resembles the New Zealand Eocene and Oligocene species of Serripecten (eg., those figured by Maxwell 1992: pi. 4) than it does S. yahliensis; it particularly resembles S. tahuianus Laws, 1935 and the unnamed LV figured by Maxwell (1992: pl.4i) in sculptural details, but differs from these species in its markedly larger size, its slightly weaker sculpture, its more widely spaced costae on the RV (than in S. tahuianus; RV not known for the unnamed species) and in having much more finely and closely serrate RV dorsal auricular margins. It therefore seems likely that S. squamocostatus is descended from the New Zealand Eocene and Oligocene coarsely sculptured species. Etymology. The specific name (Latin, ‘squama’, a scale, +‘costatus’ ribbed) reflects the coarse scaly sculpture that is diagnostic of this species. ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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