Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 5n): GS9959, J40/f6610, South Branch, Waihao River near "Pentland Hills", Bortonian (GNS)
(Pl. 5o): GS9959, J40/f6610, South Branch, Waihao River near "Pentland Hills", Bortonian (GNS)
Beu & Maxwell (1990): Chapter 7; p. 102; pl. 5 n, o.
Classification: Veneridae: Chioninae
Description: Small for family (length 7-10 mm), subtrigonal, not greatly inflated. Lunule large, impressed, lamellose; escutcheon well defined, particularly in left valve. Commarginal sculpture of very prominent, distant ridges that apparently do not bend back towards umbones. Interspaces broadly concave, weathered surfaces showing fine subsurface radial costellae. Left hinge with thin anterior cardinal tooth, narrowly triangular, bifid median cardinal tooth, and a thin posterior cardinal tooth. Right hinge with slightly curved, thin anterior cardinal tooth, a narrowly triangular bifid median cardinal tooth and a narrow, bifid posterior cardinal tooth. Pallial sinus shallow, rounded. Ventral margin finely crenulate.
Comparison: Placamen morgani (Duntroonian, Castle Hill Basin), the only described New Zealand species, is larger than the new species and has more prominent commarginal costae with recurved crests. Other records of the genus are from Pakaurangi Point, Northland (Otaian-Altonian) and Weka Pass, Canterbury (Altonian). The type species, P. placidum (Philippi, 1844), occurs in southern Australia, including Tasmania, but most extant species are from the Indo-Pacific region.
Distribution: Bortonian, South Branch, Waihao River near "Pentland Hills" (not uncommon); Raincliff Stream (uncommon).
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)