GNS Science

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

New Zealand Cenozoic Mollusca

Zeatoma impar (Powell, 1942)


(Pl. 37x): GS1579, W19/f7485, Wahanui Road, Wairoa district, northern Hawke's Bay, Opoitian (GNS)

Beu & Maxwell (1990): Chapter 14; p. 301; pl. 37 x.

Synonymy: Marshallena impar Powell, 1942, p. 83; ?= M. decens Marwick, 1931, p. 147; ?= M. celsa Marwick, 1931, p. 147; ?= M. austrotomoides Powell, 1931, p. 106; "Marshallena" impar, Beu & Maxwell 1990, p. 301, pl. 37k; Zeatoma impar, Maxwell 1992, p. 158.

Type species of Zeatoma Maxwell, 1992

Classification: Turridae: Pseudotominae

Description: Large for genus (43 mm high), tall and narrow, with moderately tall spire (equal to height of aperture and canal) and long, weakly tapered last whorl with almost parallel-sided aperture and short, straight, very widely open anterior canal lacking fasciole. Spire outline strongly stepped because of prominent shoulder angle and strongly concave sutural ramp. Sculpture of prominent, narrow, rather widely spaced axial costae, commencing abruptly at shoulder angle and extending whole height of spire whorls and onto base of first half of last whorl, becoming obsolete on last half of last whorl; crossed (without forming nodules) by low, wide spiral cords, indistinct below shoulder and on spire whorls but becoming progressively stronger lower down; entire surface covered with microscopic, closely spaced spiral threads. Outer lip thin; anal sinus shallow, widely v-shaped with a rounded apex, occupying sutural ramp. Protoconch conical, of 4.5 whorls, initially smooth but last whorl with fine spiral, and finally cancellate, sculpture.

Comparison: The distinction from Zeatoma decens (Ormond Formation, Gisborne, Opoitian) and Z. austrotomoides (Waihi Beach, Hawera, Waipipian) is subtle and, when adult shells are compared, seen to be probably unrealistic; more material is needed of these rather uncommon species to understand their taxonomy. The distribution (above) assumes that at least these three nominal taxa are conspecific. This is one of the latest members of a group of mid-late Cenozoic species belonging in Zeatoma, distinguished from Marshallena above, under M. neozelanica (Pl. 8 v). An unnamed, younger species differing from Z. decens = Z. impar in having prominent spiral cords occurs in diverse molluscan assemblages of mid-shelf facies in the Mangahao district, west of Pahiatua, northern Wairarapa (Mangapanian).

Distribution: Opoitian-Waipipian; GS2329, hill north of Whetukura, c. 3 km southeast of Ormondville, Dannevirke district, southern Hawke's Bay, Waipipian (type of M. impar); uncommon in mid-outer shelf soft-bottom facies (blue-grey sandy mudstone) in the Wairoa district, northern Hawke's Bay (Opoitian-Waipipian), in shallow-water sandstone along the Wanganui-South Taranaki coast (Waipipian) and in the Awatere Valley, Marlborough (Waipipian), and in the Birch's Mill shell lens at Te Waewae Bay, Southland (early Opoitian).

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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