Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 9m): holotype, GS3892, J42/f6573, right bank, Kakanui River near mouth, Whaingaroan (TM5472, GNS)
Beu & Maxwell (1990): Chapter 9; p. 134; pl. 9 m.
Synonymy: Cirsotrema (Cirsotrema) gagei Maxwell 1978, p. 36
Description: Size moderate for genus (height probably about 65 mm), high-spired. Apical whorls missing from only known specimen, 5.5 strongly convex whorls remaining; last whorl with a well defined basal disc. Sutures obscured by fusion of axial costae with suprasutural cord and costae on previous whorl. Axial sculpture of slightly prosocline, blade-like costae, each composed of several (typically about 6) thin lamellae fused together, reaching from suture to suture on spire, and extending across base of last whorl to aperture. Very prominent, rounded varices, narrowing posteriorly and composed of very numerous fused lamellae, at irregular intervals; 16 costae and varices on penultimate whorl. Spiral sculpture, apart from a suprasutural cord that emerges on last whorl as peribasal keel, consisting of very fine, weakly impressed grooves and occasional low, broad, subdued cords between axial costae; about 5 on last whorl. Aperture oval, peristome complete, varix prominent; fasciole, if present, hidden by inner lip.
Comparison: This highly distinctive species differs from "typical" New Zealand members of Cirsotrema, e.g. C. lyratum (Pl. 141) and C. kuriense (Pl. 6c), in having very thin axial costae and very feeble spiral sculpture. C. (Tioria) youngi (Pl. 4n) also has thin costae and weak spiral sculpture, but it lacks definite varices, and has a distinct fasciolar ridge. C. gagei occurs with C. lyratum at Kakanui River.
Distribution: Whaingaroan, McDonald Limestone, Kakanui River, near mouth (type).
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)