GNS Science

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

New Zealand Cenozoic Mollusca

Semicassis (Kahua) skinneri (Marwick, 1928)


(Pl. 37c): holotype, GS10193, CH/fl06, Whenuataru Tuff, tip of Tarawhenua Peninsula, Pitt Island, Chatham Islands, Waipipian (TM6814, GNS)

Beu & Maxwell (1990): Chapter 14; p. 295; pl. 37 c.

Synonymy: Phalium (Kahua) skinneri Marwick 1928, p. 482

Type species of Kahua Marwick, 1928

Classification: Cassidae: Phaliinae

Description: Moderate- sized for family (41-58 mm high), subspherical, with low, conic spire, very large, enveloping last whorl, and very short, deeply notched, very strongly twisted anterior canal separated from last whorl by deep, narrow groove, forming a very prominent, ridge-margined fasciole. Sculpture of many low, wide, flat- topped, closely spaced spiral cords, 4 or 5 on spire whorls and about 23 on last whorl, those on sutural ramp bearing many fine, close, prominent spiral lirae; on most specimens, 1 wide cord at base of sutural ramp is a little more prominent than others and bears a row of low nodules. On small specimens, spiral cords cross many narrow, prominent, closely spaced axial costae (about 40 on last whorl of holotype) but on large shells, costae are absent from all but sutural ramp of last whorl. Aperture large, oval, strongly thickened; outer lip a very thick, rounded varix, with about 20-26 low, narrow, short ridges down inside edge; inner lip prominently ridged with many anastomosing wrinkles on inner columellar area. Protoconch conical, of 2.5 smooth, inflated whorls.

Comparison: The Chatham Islands species Semicassis skinneri differs from the coeval mainland species S. fibrata (type species of Mauicassis Fleming, 1943) only in its more numerous, narrower spiral cords and smaller nodules on the shoulder angle, and in our opinion Kahua Marwick, 1928 is the same group as Mauicassis Fleming, 1943 (with which Abbott (1968, p. 117) synonymised Liracassis Moore, 1963; but in our opinion Kahua and Liracassis have evolved independently from Echinophoria in the southern and northern hemispheres, respectively). Large shells of S. fibrata have very similar, strongly thickened, lirate apertures to that of S. skinneri. The status of this group and whether it should be treated as a subgenus of Semicassis or a full genus must await fuller consideration of the range of characters and classification of Semicassis, but it seems likely that Kahua (= Mauicassis) and Liracassis are both genera separate from Semicassis and Echinophoria.

Distribution: Opoitian-Waipipian; Whenuataru Tuff, northern Pitt Island, Chatham Islands, Waipipian (type); uncommon (most specimens are fragmentary) in Whenuataru Tuff on the tip of Tarawhenua Peninsula, Pitt Island (Waipipian-Mangapanian), and rare in Birch's Mill shell lens (early Opoitian), Te Waewae Bay, Southland.

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)


Back to index page