GNS Science

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

New Zealand Cenozoic Mollusca

Hormomya (?) willetsi (Marwick, 1928)


(Pl. 3e): holotype, GS10191, CH/f104, sea-cliffs near Waitangi radio station, Chatham Island, Waipawan (?) (TM4180, GNS)

Beu & Maxwell (1990): Chapter 6; p. 89; pl. 3 e

Synonymy: Mytilus (Aulacomya) willetsi Marwick 1928, p. 444-445; Aulacomya willetsi; Septifer willetsi

Classification: Mytilidae: Mytilinae

Description: Small for family (height 9-17 mm), mytiliform. Dorsal margin long, straight, weakly alate. Shell strongly inflated medially, with moderately well defined dorsal and ventral areas. Radial sculpture of low, rounded costae medially; dorsal and ventral areas with similar but somewhat divergent costae, some of which are radial, others branching off the main ribs. Commarginal sculpture of fine costellae in intercostal spaces, and growth ridges. Internal features not known, but umbonal septum apparently absent.

Comparison: The affinities of this little mytilid are uncertain, but its overall size, shape and sculpture and its association with warm-water molluscs make assignment to the cool-water genus Aulacomya unlikely. It is superficially similar to some species of Septifer (see below) but no trace of an umbonal septum — the diagnostic character of that genus — could be observed in any of the available material, possibly because of the rather poor preservation of most specimens. It is here tentatively included in Hormomya, species of which resemble Septifer, but lack a septum.

Distribution: Waipawan(?), Red Bluff Tuff, sea-cliffs near radio station, Waitangi, Chatham Island (type) (common).

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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