Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 7i): GS11214, J42/f126, Bridge Point, Kakanui, Runangan (GNS)
Beu & Maxwell (1990): Chapter 8; p. 115; pl. 7 i.
Synonymy: Pecten venosum Hutton, 1873b, p. 30; Chlamys venosa
Description: Small for genus (height 35-40 mm), right valve more inflated than left. Ears prominent, dorsal margins on right valve serrate, divergent, byssal notch well developed; dorsal margins on left valve colinear. Radial sculpture on disc of right valve of 10-13 prominent convex primary costae commencing at or near apex, those near dorsal margins scaly at an early stage of growth, others remaining smooth until 25-30 mm from apex when they become sparsely scaly. From 1-3 finely scaly secondary costellae appearing between costae at 20-25 mm from apex, and "tertiary" ones at a somewhat later stage, some of them arising from flanks of primary costae. Radial sculpture on left valve more variable than on right, some shells with primary costae remaining very prominent throughout growth; in others becoming narrower and of Tower relief and even subdividing, and eventually becoming similar in strength to interstitial costellae, so there may be 85 or so subequal scaly costae distally. Ears of both valves with 5 or 6 fine, scaly radial costae.
Comparison: Serripecten venosus belongs to a complex and poorly understood group of pectens of Late Eocene to Early Oligocene age, particularly well represented in the limestones and associated tuffs of North Otago. It is easily distinguished from the other species, most of which are undescribed, by having relatively few prominent primary costae that remain smooth throughout most of their growth, lacking the lateral spine-like scales that charactersie Serripecten. The costae are also similar (but not identical) on the two valves, so the generic position is suspect. This seems to be part of the group (unnamed genus?) mentioned in Notochlamys(?) by Beu & Maxwell (1990, p.131), but it probably belongs in neither Notochlamys nor Serripecten.
Distribution: Runangan, "Oamaru" (type), possibly from Waiareka Volcanic Formation, Bridge Point, Kakanui where it is common; Trig M, Totara; Teschemaker's Quarry.
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)