GNS Science

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

New Zealand Cenozoic Mollusca

Atamarcia benhami (Marwick, 1927)


(Pl. 36a): mouth of Inaha Stream, South Taranaki, Waipipian (GNS, ex F.D. Chambers Collection)


(Pl. 36b): mouth of Inaha Stream, South Taranaki, Waipipian (GNS, ex F.D. Chambers Collection)

Beu & Maxwell (1990): Chapter 14; p. 285; pl. 36 a,b.

Synonymy: Venus sulcata Hutton 1875, p. 458 (not of Lamarck, 1835); Cytherea (Circomphalus) sulcata; Eumarcia (Atamarcia) benhami Marwick 1927, p. 631 (new name for Venus sulcata Hutton, preoccupied); Beu & Maxwell 1990, p. 285, pl. 36a, b

Classification: Veneridae: Tapetinae

Description: Moderately large for genus (65-77 mm long), elongate- oval, umbo at anterior third of length; only moderately inflated; with smooth interior ventral margin; lunule deeply impressed, smooth, long and narrow, not marked off by a groove. Exterior sculptured with many prominent, smooth, relatively widely spaced, commarginal ridges, strongly convex on ventral side and weakly concave on dorsal side, the lamellar outer dorsal edge often broken and appearing frilled; separated by deep grooves equal in width to ridges. Hinge relatively narrow, with very long, narrow, ligamental nymph and deep escutcheon in each valve, a prominently grooved posterior cardinal tooth and thin, simple, median and anterior cardinal teeth in right valve, and a long straight posterior cardinal tooth, a thick, grooved median cardinal tooth and a triangular, undivided anterior cardinal tooth in left valve. Adductor scars large, almost equal; anterior pedal retractor scar separate from adductor, deeply impressed above it, a prominent facet just in front of anterior cardinal tooth. Pallial sinus deep, reaching almost half length, curved slightly upward, obliquely truncated.

Comparison: Atamarcia benhami is easily identified by its low, oval shape and by having much the most prominent commarginal sculpture of all New Zealand Atamarcia species; all its older relatives have shallower commarginal grooves. At many Pliocene localities, A. benhami occurs with (but is much less common than) Eumarcia plana. The extinctions of Eumarcia and Atamarcia are useful biostratigraphic indices of the end of Nukumaruan time.

Distribution: Kapitean-Nukumaruan; "Napier, in limestone" (type; Hutton 1875, p. 458), presumably Scinde Island Limestone at Napier, Hawke's Bay (Nukumaruan); moderately common in shallow-water, soft-bottom facies and diverse molluscan assemblages, in Wanganui basin (Pliocene, shellbeds at Waipipi, Mangapani, and Wilkies Bluff), in the Gisborne district (Tokomaru Sandstone facies of Tolaga Bay to Anaura Bay, Kapitean), in Hawke's Bay (moderately common in soft sandy facies of Mangapanian and Nukumaruan limestone) and in southern Wairarapa (rarely in Pukenui Limestone of the Maungaraki Range).

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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