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Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)

New Zealand Cenozoic Mollusca

Megacardita ponderosa (Suter, 1913)


(Pl. 12i, j): Shell Gully, Chatton, Duntroonian (GNS, ex C.R. Laws Colln)

Beu & Maxwell (1990): Chapter 10; p. 148; pl. 12 i, j.

Synonymy: Venericardia ponderosa Suter 1913b, p. 296; V. (Megacardita) ponderosa; V. caelebs Marwick 1929, p. 911; V. (Megacardita) caelebs

Classification: Carditidae: Venericardiinae

Description: Large for family (length 65-85 mm), subelliptical, beaks close to anterior end. Posterior area rather narrow, shallowly concave. Lunule relatively small, smooth, strongly pouting. Radial sculpture of 26-29 prominent costae of variable shape and spacing, in some specimens squarish-sectioned with relatively broad interspaces (as wide as costae in some shells), on others rounded or broadly triangular with narrow interspaces. Anterior ribs finely scabrous (particularly proximally), others smooth or with fine growth lines. Costae on middle part of posterior area considerably weaker than elsewhere. Hinge heavy, left valve with prominent triangular anterior cardinal tooth, widely separated from a long, narrow, slightly curved posterior cardinal. Right hinge with anterior cardinal fused to lunule, and a very broad, somewhat excavated median cardinal.

Comparison: Megacardita includes relatively large, elongate venericardiines with anteriorly placed beaks. The only other New Zealand species of the genus — which also occurs in the mid-Cenozoic of Europe and Africa — is M. squadronensis (Otaian, Waiheke and Kawau Islands); this differs from M. ponderosa in having flattened ribs with narrow interspaces.

Distribution: Duntroonian; Chatton Formation, Muddy Terrace, Waikaia, Southland (type locality of V. ponderosa); Shell Gully, Chatton (type locality of V. caelebs) (rare); Wendon Valley, moderately common; Wharekuri Greensand, Wharekuri (rare). V. caelebs was based on an immature specimen only 30 mm long. Adult topotypes are considered to fall within the limits of variation of M. ponderosa.

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
ISBN 978-0-478-19705-1
ISSN 1177-2441
(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)


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