Notochlamys nanarupensis 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. 58, figs. 15E, 16G, H]
2001 Notochlamys nanarupensis Beu & Darragh, 2001
A. G. Beu & T. A. Darragh, 2001, figure 16.
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«Description. Moderately large for genus (to c. 56 mm high), almost equidimensional, slightly prosocline, RV slightly more inflated than LV; umbonal angle c. 105º; initial umbonal angle moderately narrow, but dorsal margins strongly concave (curved outwards) to produce wider umbonal angle as shell grows; posterodorsal margin significantly longer than anterodorsal margin. Sculptured with 17-19 evenly rounded but low, relatively narrow, radial plicae (or relatively large, smooth, evenly rounded costae), weakly subdividing on some specimens, particularly near anterior and posterior ends of disc, where plicae are lower, narrower and more closely spaced than elsewhere; crossed only by very fine antimarginal ridgelets and weak commarginal growth ridges; one paratype bears obvious, fine shagreen .microsculpture over antimarginal ridgelets in interpjical spaces. Anterior auricles large, elongate; on RV with deep byssal notch and functional ctenolium (with c. 5 narrow,, elongate teeth) and wide, deeply impressed byssal fasciole, bearing coarser commarginal growth ridges than remainder of shell; main auricle face above fasciole sculptured with 3 - 4 moderately high, narrow radial costae over lower half of main auricular surface only, costae crossed by even, regular, closely spaced, moderately high commarginal lamellae; on LV tall, with anterior margin very weakly sinuous and inclined strongly towards anterior, sculptured with 4 - 5 very weak, widely spaced radial costae but without commarginal lamellae. Posterior auricles very short, with posterior margin slightly concave and inclined strongly towards anterior, sculptured with only 1 or 2 very low, narrow radial costae on each valve margin. Dorsal margin of RV anterior auricle raised well above hinge line in irregular, weakly convex outline, weakly serrated by commarginal lamellae. Hinge of RV with low, narrow, resilial and dorsal teeth; LV hinge not seen. Interior of ventral margin smooth, without internal rib carinae.
Dimensions.
Type material. Holotype, WAM 69.235, Nanarup Limestone Member of Werillup Formation (Aldingan, Late Eocene), PL508, Nanarup Lime Quarry, near Albany, southern Western Australia, coll. O. Thorne, 10.iii.I969; paratype, WAM 69.234, all data as above; WAM 72.46a-e, 5 paratypes, data as above, coll. G. W. Kendrick, 25.i. 1972; paratype, WAM 94.712, data as above, coll. K. J. McNamara, 1990-1993.
Other material examined. Aldingan: NANARUP Limestone: PL508, Nanarup Quarry (8 specimens); PALLINUP SILTSTONE : WAM 76.1234, small quarry by fence line, headwaters of Mungliginup Creek, near Esperance, WA, map ref. SI/51-6/564817 (partial mould, with similar costae to N. nanarupensis, and with fine shagreen all over; auricles missing and disc shape not determinable)
Occurrence and time range. Known with certainty only from the type locality (Late Eocene); an incomplete mould from Pallinup Siltstone (also Late Eocene) in southern Western Australia probably belongs here also.
Remarks. The new species is clearly a very aberrant member of Notochlamys, if referable there at all. One paratype (WAM 72.46d, a nearly complete RV; Fig. 15E) bears obvious, if fine, shagreen microsculpture in the interplical spaces, but the specimen is rather atypical of N. nanarupensis; it is a little more inflated than the other material, and the margins of the strongly rounded costae (or narrow plicae) are more sharply defined than in all other specimens. Nevertheless, with 18 narrow, strongly rounded, smooth plicae on an RV with the same shape of anterior auricle as the paratype WAM 69.234, it seems likely to be conspecific with the other material from the same locality. All the material is distinguished from the other species referred here to Notochlamys by its markedly narrower and more numerous plicae, by having only one order of radial sculpture, and by having a rather wider shape. In the absence of knowledge of the LV preradial dissoconch microsculpture (always impossible to see on material from limestone, and particularly difficult on Eocene material) the taxonomic position of this species will remain tentative, but it makes a plausible early, ancestral species of Notochlamys.
Etymology. The specific name ( ‘from Nanarup’ [Quarry]) refers to the type locality of the species.»
ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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