Notochlamys kendricki 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. 63, figs. 16A-F]
2001 Notochlamys kendricki Beu & Darragh, 2001
A. G. Beu & T. A. Darragh, 2001, figure 16.
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«Description. Average-sized for genus (most 4 0 - 45 mm high, reaching 55 mm), very weakly to quite obviously prosocline, umbonal angle narrow (95- 100°); valves almost equally inflated—proximal area of disc slightly more inflated on RV than on LV, central area of disc slightly more inflated on LV than on RV. Sculpture of 7 or 8 extremely prominent, high plicae, each plica as wide as 2 plical interspaces on RV, with vertical to slightly undercut sides on RV, markedly narrower on LV than on RV, almost as high as wide on LV; plical crests weakly rounded on RV of most specimens, becoming slightly lower and more rounded on distal disc of large specimens, weakly sculptured to polished and almost smooth on proximal area of many specimens; strongly rounded on LV; radial costae low, almost smooth, 4 on plical crests of most RVs, up to 6 on distal disc of large specimens; 3 weak ones developing on plical crests of LV over distal disc of medium-sized specimens; 3 weak costae developing in RV interplical spaces over distal disc of medium-sized specimens and 3-6 in LV interspaces, all becoming prominent on distal third to half of disc on large shells; interplical spaces, plical sides and auricles bearing even, uniform, relatively fine shagreen microsculpture, forming a complete secondary surface, including on plical crests of some small unabraded specimens. Anterior auricles large, elongate, on RV with deep byssal notch and functional ctenolium retained in largest adults; posterior auricles small, short, with almost vertical posterior margins, posterior margins weakly concave in some specimens. Weak growth ledges present over distal third of disc of some specimens. Hinge with prominent resilial and dorsal teeth in RV, and corresponding resilial sockets in LV. Weak internal rib carinae commencing at about 35-40 mm disc height, becoming prominent on plical margins over distal third of large specimens.
Dimensions-
Type material. Holotype, WAM 81.887a, Roe Calcarenite (Late Pliocene), basal 0.6 m of carbonate sand, in pit 0.5 km N of Hampton microwave repeater tower, Madura district, Roe Plains, Eucla Basin, coll. V. A. Ryland & G. W. Kendrick, 29.ix-4.x.l980; one paratype WAM 81.887b in same lot as holotype; 8 paratypes, WAM 79.1008a-h, 1.5 km N of Hampton Tower, basal 0.4 m carbonate sand, coll. V. A. Ryland & G. W. & W. E. Kendrick, 5-13.viii.1978; NMV P302790, one paratype, PL3167, pit 1.5 km N of Hampton Tower, coll. T. A. Darragh, 29.ix.1980.
Other material examined. Late Pliocene: ROE CALCARENITE: WAM 79.1002, 79.1003a-l, pit 1.5 km N of Hampton Tower, basal 0.4 m carbonate sand (13 specimens); WAM 94.836a-i, all data as holotype (9 specimens); WAM 81,607a, b, all data as holotype (2 specimens); WAM 79.1002, all data as holotype (one articulated pair); WAM 81.554, from mixed spoil, pit 0.5 km north of Hampton Tower (one articulated pair); AMS C90093, PL3172, Hampton Tower (3 specimens); NMV PL3167, pit 1.6 km N of Hampton Tower (10 specimens).
Occurrence and time range. The only records with precise stratigraphic data are from the basal 0.6- 0.4 m of carbonate sand at and near the type locality, Roe Calcarenite (Late Pliocene), Roe Plains, southeastern Western Australia; the other material is not localised stratigraphically within the Roe Calcarenite
Remarks. It is with a certain amount of hesitation that we separate Notochlamys kendricki sp. nov. from N. hexactes. The differences are slight, but constant. The most obvious distinction is in the number, width and prominence of the plicae which, although in N. kendricki only slightly more prominent than those of the most extremely coarsely plicate specimens of N. hexactes (notably the holotype; Dijkstra 1995: pl. 30, figs 130, 131), are consistently very prominent in N. kendricki, are raised higher above their interspaces, and have more nearly vertical to slightly undercut edges than in most specimens of N. hexactes. They are also a little wider on the RV, and correspondingly narrower on the LV, quite consistently in N. kendricki than in the most extreme N. hexactes. Also, presumably as a result of the narrower interspaces, there tends to be one more plica than on specimens of N. hexactes of the same size and proportions. A further distinction that seems to be constant is the markedly shorter posterior auricles of N. kendricki than of N. hexactes. Specimens of N. kendricki are also significantly to strongly prosocline in shape, in contrast to the very weakly prosocline to acline N. hexactes. Specimens of N. kendricki also tend to be significantly taller and narrower (with a narrower umbonal angle) than specimens of N. hexactes, although this difference is not constant. The few large specimens of N. kendricki we have seen, having concave, outwardly flared anterodorsal and posterodorsal margins, become wider and markedly more strongly prosocline than smaller specimens. Because of the very weak radial costae of most of the western (anguineus form) specimens of N. hexactes, the new species more nearly resembles the eastern (tasmanica) form, but specimens of this form tend to have lower plicae and much more prominent radial costae than N. kendricki.
There can be no doubt that N. kendricki is correctly assigned to Notochlamys, and its abundance in the basal carbonate sand of Roe Calcarenite makes it quite surprising that Notochlamys is otherwise almost unknown as a younger fossil in southern Australia. In particular, Hallett Cove Sandstone and Norwest Bend Formation in the St Vincent and Murray basins, respectively, are very similar to Roe Calcarenite in depth of deposition (all are very shallow-water, near-shore deposits) and in their faunal content, sharing almost all the same pectinids. The only obvious difference is that Roe Calcarenite is, as the name indicates, an unconsolidated limestone, lacking the terrigenous sand that is dominant in Hallett Cove Sandstone and Norwest Bend Formation. Even within Roe Calcarenite, N. kendricki has been collected only in the Hampton microwave tower area, perhaps reflecting the depth of the fossiliferous unit below the ground surface. The upper surface of Roe Calcarenite is a very hard calcrete sheet 30 cm thick, and the weathering and lithification decrease downwards; the unlithified basal carbonate sand is exposed in pits near the Hampton tower in uncomformable contact with a wave-planed surface of Abrakurrie Limestone. However, Amusium balloti is another pectinid that is present in Hallett Cove Sandstone and Norwest Bend Formation but, surprisingly, is absent from Roe Calcarenite, suggesting that these occurrences have an ecological explanation; Notochlamys and Amusium might well have different tolerances to sediment type and turbidity from other pectinids. However, it remains surprising that we know of no records of Notochlamys from Pliocene rocks of the Otway and Gippsland basins. Etymology. We have great pleasure naming this species in honour of our colleague George W. Kendrick, Research Associate at the Western Australian Museum, to record his long, devoted research on the Cenozoic Mollusca of Western Australia and, in particular, on the Roe Calcarenite, and as an acknowledgement of the considerable assistance rendered to us for this paper.»
ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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