Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 20l): GS951A, J41/f8475, Target Gully Shellbed, Oamaru, Altonian (GNS)
Beu & Maxwell (1990): Chapter 11; p. 188; pl. 20 l.
Synonymy: Calyptraea (Sigapatella) maccoyi Suter 1917, p. 9
Description: Size moderate for genus (diameter 15-25 mm), cap- shaped, apex strongly excentric, near margin; with internal septum and highly excentric umbilicus. Protoconch of about 1.5 smooth whorls. Teleoconch of 1.5-2 whorls, early part with fine spiral threads, later part with prominent, rather irregular cords, interrupted by growth ridges, mostly more or less spiral, but some divergent; 11-15 cords distally. Well preserved shells with an overlay of numerous very fine discontinuous spiral threads.
Comparison: Sigapatella subvaricosa (Waiheke Island, Otaian) is very similar to S. maccoyi and may not be distinct, but it seems to have spiral cords that are more discontinuous than those of S. maccoyi. An undescribed species from Lorne, North Otago (Kaiatan) has spiral rows of small tubercles and has a superficial resemblance to some species of Haliotis. Other New Zealand Sigapatella species are either devoid of spiral sculpture or have only fine threads. Marshall (2003) revised the Recent species and a few late Neogene species of Sigapatella, synonymising the genus Zegalerus with Sigapatella, and distinguishing species by subtle protoconch differences that have not been studied in pre-Nukumaruan fossils. Undoubtedly many species remain unrecognised at present, as in the other major calyptraeid genera, Maoricrypta and Grandicrepidula.
Distribution: Duntroonian?, Altonian; Mount Harris Formation, Awamoa, Oamaru, Altonian (type) (rare); Target Gully Shellbed (moderately common); ?Whitewater Creek, Castle Hill Basin, Duntroonian.
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)