Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 40g): shellbed on north bank of Mangahao River 1.6 km south of Mangahao, northern Wairarapa, Nukumaruan (M33633, National Museum of N.Z.)
(Pl. 40h): shellbed on north bank of Mangahao River 1.6 km south of Mangahao, northern Wairarapa, Nukumaruan (M33633, National Museum of N.Z.)
Beu & Maxwell (1990): Chapter 15; p. 316; pl. 40 g,h.
Synonymy: Eumarcia plana Marwick 1927, p. 627; Eumarcia (Eumarcia) plana, Beu & Maxwell 1990, p. 316, pl. 40g, h.
Classification: Veneridae: Tapetinae
Description: Large for genus (60-100 mm long), elongate-oval, with low umbo at anterior quarter of length; lunule only a slightly concave area, not marked off by groove; interior ventral margin smooth; exterior smooth and polished except for weak growth lines. Hinge narrow; right valve with long, low, weak, posterior cardinal lamella on nymph edge and 3 other almost equally long, more anterior cardinals, the median and posterior ones grooved; left valve with 3 prominent cardinal teeth only, the posterior one not separated from nymph by a groove, the median one deeply grooved. Anterior adductor scar small, oval; posterior adductor scar of similar shape to but much larger than anterior one. Pallial sinus short but deep, with pointed anterior end a short distance in front of posterior adductor scar.
Comparison: Eumarcia plana is much the most common and widespread large, smooth Eumarcia species in New Zealand; the South Canterbury species E. pareoraensis (Otaian-Altonian) is smaller and more elongate, and other Eumarcia species are rare. Species of the similar genus Atamarcia have a sunken, groove-bounded lunule, and many have prominent commarginal sculpture (see A. thomsoni, Pl. 28e and A. benhami, Pl. 36a, b).
Distribution: Waipipian-Nukumaruan; "boat-landing, Nukumaru" (i.e., Nukumaru Beach, west of Wanganui, almost certainly from Nukumaru Brown Sand), Nukumaruan (type); abundant in relatively few shallow-water, near-shore, soft-bottom facies, particularly in some Nukumaruan limestone beds in Hawke's Bay, and in the Waipipi Shellbeds (Waipipian), Waverley Beach, and the Nukumaru Brown Sand (Nukumaruan), Nukumaru Beach, both west of Wanganui; also found in other Waipipian-Nukumaruan shellbeds and limestone in Wanganui, Hawke's Bay, Wairarapa, North Canterbury, and Titirangi, Chatham Islands (Nukumaruan). The extinction of the genus in New Zealand is a useful marker of the end of Nukumaruan time.
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)