Notochlamys squamundata 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. 59, figs. 15A-D, F-H]
2001 Notochlamys squamundata Beu & Darragh, 2001
A. G. Beu & T. A. Darragh, 2001, figure 15.
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«Description. Average-sized for genus (40-50 mm high), moderately inflated, inflation of RV about equal to LV; umbonal angle moderately narrow, 95-105º; with c. 10 evenly rounded plicae, apparently in most specimens consisting of an initial 5 plicae, each subdividing early on the disc; acline to slightly prosocline. Radial costae low, fine, numerous, c. 7-10 on each plica on central area of disc, fewer on narrower, anterior and posterior plicae, 3-5 in interplical spaces; secondary and tertiary costellae subdivided and intercalated down disc to maintain costal proportions and spacing; all bearing obvious, low, closely spaced, ventrally directed scales over entire disc and auricles. Interplical spaces and, on some specimens, costal interspaces on and between plicae on distal area of disc bearing low, fine but obvious shagreen microsculpture, one specimen with shagreen raised into secondary shell surface over plicae on proximal two thirds of disc. Anterior auricles large, elongate, with deep byssal notch and functional ctenolium in RV, but slightly to severely incomplete in all available material; posterior auricles small, short, with weakly concave posterior margin. Hinge (visible only in paratype, RV, WAM 88.810c) with narrow but obvious resilial and dorsal teeth; interior of ventral margin without internal rib carinae.
Dimensions.
Type material. Holotype, NMV P302636, Port Willunga Formation (Janjukian), PL3293, quarry and cliffs north of jetty at Stansbury, Yorke Peninsula, South Australia, grid ref. Stansbury 554344, coll. T. A. Darragh, 29.iv. 1996; one paratype, NMV P302863, same data; two paratypes, SAM T968B, C, two of Tate’s (1886) unfigured paralectotypes of Pecten consobrinus Tate, from ‘mouth of Onkaparinga River’, Port Willunga Formation, late Eocene (Aldingan), near Adelaide, South Australia; three paratypes, WAM 88.810a-c, Port Willunga Formation, (Willungan, Oligocene), 200 m south of Onkaparinga Trig., Onkaparinga, near Adelaide, South Australia, coll. K. J. McNamara, 23.iii.1986.
Other material examined. Janjukian: JAN JUC FORMATION: Bird Rock ledge, Torquay (1 specimen); PORT WILLUNGA FORMATION: PL3292, Wool Bay (1 specimen); PL3293, Stansbury (2 specimens). Longfordian: MELTON LIMESTONE: PL3295, Myponie Point (8 specimens); PL3296, Black Rock (11 specimens); fragmentary specimens from ABRAKURRIE LIMESTONE, Eucla Basin: WAM 65.646, Mullamullang Cave, near Madura, c. 1.6 km in from entrance, 100 m below surface (1 specimen); WAM 68.112, Mullamullang Cave, at bottom of entrance, not in situ (one RV); WAM 68.125, Mullamullang Cave (one fragment); WAM 68.320, Murra-el-elevan Cave (1 specimen).
Material illustrated by Ludbrook (in Lowry 1970: fig. 211, J), under the name Notochlamys antecedens Singleton, from Abrakurrie Limestone at Murra-el-elevan Cave and Firestick Cave, Nullarbor Plain, seems likely to be based on further records of N. squamundata. However, we have not seen all the material (in GSWA) and it has some similarities to Semipallium foulcheri, so these records need confirmation.
Occurrence and time range. Aldingan(?) to Longfordian. Most material is from St Vincent Basin; fragmentary specimens from Abrakurrie Limestone in the Eucla Basin and one from Torquay, Port Phillip Basin, Victoria.
Remarks. Most of the material assigned to Notochlamys squamundata sp. nov. bears the distinctive character of finely but closely and obviously scaly radial costae, which distinguishes this species from all other species we assign to Notochlamys. However, one paratype, NMV P302863, from the same lot as the holotype, lacks radial costae altogether, and simply has smooth, evenly rounded plicae of high amplitude, evenly sculptured with fine shagreen all over. The one specimen from Jan Juc Formation at Torquay that we assign here is very similar to this smooth paratype, but develops weak radial costae around the ventral margin of the disc. Not a single one of the specimens assigned here, however, is well enough preserved for the LV preradial dissoconch sculpture to be visible, so the whole lot, including the type material, is assigned here purely on gross morphology. It appears reasonable, though, to assign this species to Notochlamys, and there is certainly no other genus known to us from Australia that would be appropriate for it. The fragmentary specimens from Abrakurrie Limestone, in particular, can be assigned to Notochlamys only tentatively, as none has even a reasonable fragment of an auricle, but the disc sculpture seems to lie within the range of variation of the Port Willunga Formation material. Notochlamys (?) squamundata differs from Semipallium foulcheri in all specimens having fewer, wider and more prominent plicae, and in most specimens having weaker radial costae, a larger size, and a less markedly prosocline disc shape than those of S. foulcheri. Also, a markedly higher proportion of specimens of N. squamundata has shagreen microsculpture than in S. foulcheri, in which shagreen is rare. In some cases the distinction is far from obvious and deserves more study.
Etymology. The specific name (Latin, ‘squameus’, scaly + ‘undata’, undulating, referring to the radial plicae) indicates the fine scaly sculpture on most specimens referred to the new species.»
ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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