Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 9b): holotype, probably from lower gorge, Porter River, Castle Hill Basin, Canterbury, Whaingaroan (TM2856, GNS)
(Pl. 9f): holotype, probably from lower gorge, Porter River, Castle Hill Basin, Canterbury, Whaingaroan (TM2856, GNS)
Beu & Maxwell (1990): Chapter 9; p. 131; pl. 9 b, f.
Synonymy: Ostrea subdentata Hutton 1873b, p. 48; O. (Eostrea) subdentata; Notostrea subdentata; Ostrea (Notostrea) subdentata
Type species of Notostrea Finlay, 1928
Classification: Gryphaeidae: Pycnodonteinae
Description: Small for genus (height 25 mm), ovate-trigonal, known definitely only by the moderately inflated lower (left) valve. Attachment area small, no sculpture apart from irregular growth ridges and welts. Ligamental area rather small, with a relatively large, shallow resilifer. Commissural shelf narrow, bearing distinct chomata. Adductor muscle scar small, subcircular, much closer to hinge than to ventral margin.
Comparison: Pycnodonte subdentata differs from P. (Notostrea) tarda (Pl. 3b, c) in its smaller size, its less inflated left valve, and its much stronger chomata. Although no unequivocal evidence for vesicular shell layers - the diagnostic character of the Pycnodonteinae, and present in P. tarda - could be discerned in the available material, the similarity of P. subdentata to P. tarda in shell shape and in the shape and position of the adductor muscle scar indicates that these species are closely related. As noted above under P. subdentata, Notostrea is probably an earlier name for Phygraea Vyalov, 1936.
Distribution: Whaingaroan, "Broken River (Lower beds)" (type probably from marls below limestone (Coleridge Formation), lower gorge of Porter River, Castle Hill Basin). Not definitely recorded elsewhere, but possibly present in Cobden Limestone, Greymouth (Whaingaroan?) and in marls of similar age in Te Kuiti district.
Cite this publication as: "A.G. Beu and J.I. Raine (2009). Revised
descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990). GNS
Science miscellaneous series no. 27."
© GNS Science, 2009
(Included with a PDF facsimile file copy of New Zealand Geological Survey Paleontological Bulletin 58 in CD version from: Publications Officer, GNS Science, P.O. Box 30368 Lower Hutt, New Zealand)