GNS Science

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

New Zealand Cenozoic Mollusca

Cirsotrema (Cirsotrema) lyratum (Zittel, 1864)


(Pl. 14l): Waitaki River, opposite Wharekuri, Duntroonian (GNS, ex Suter Collection)

Beu & Maxwell (1990): Chapter 10; p. 164; pl. 14 l.

Synonymy: Scalaria lyrata Zittel 1864, p. 41; Scalaria browni Zittel 1864, p. 42; S. rugulosa "Sowerby" (not of Sowerby, 1846); S. rugulosa lyrata; Epitonium (Cirsotrema) rugulosum lyratum; E (Cirsotrema) lyratum; Cirsotrema browni

Classification: Epitoniidae

Description: Rather large for family (height 45-85 mm), spire very elevated. Protoconch not known. Teleoconch of at least 10 strongly convex whorls; sutures obscured by fusion of adapical ends of axial costae to supramargining cord on previous whorl. Last whorl with well-developed basal disc, its outer edge well below periphery, flat except for narrow fasciole adjacent to aperture. Axial sculpture of prominent, prosocline costae composed of numerous lamellae fused together, convex or almost flat on front (adapertural) face, concave behind. Varices at irregular intervals, typically markedly thicker than costae, with from 1-13 costae between each pair of varices; 13-15 axials per whorl. Costae and varices slightly excavated adapically, with a small spine on edge of sulcus; all axials extending across base to fasciole. Spiral sculpture of 6-8 narrow, low cords that surmount axials, with fine threads in between, the latter reticulated by growth lines. Cord margining lower suture emerging on last whorl as edge of basal disc Aperture circular, peristome continuous, basal lip slightly truncate.

Comparison: Cirsotrema lyratum is recorded very widely from throughout the North and South Islands, particularly from glauconitic sandstone and from limestone. Many of the records appear, however, to refer to other species. C. lyratum is here restricted to relatively large specimens in which the varices are noticeably more prominent than the costae, and the spiral cords are relatively strong and surmount the axials. Unfortunately, the limits of the species are very uncertain. C. kuriense (Pl. 6c) and C. caelicola (Altonian, Kakanui) have varices that are barely distinguishable from the costae. In C. gagei (Pl. 9m) the costae are blade-like, the varices are much more massive than the costae, and the spiral sculpture is very weak, but it is possible that C. caelicola intergrades with C. lyratum.

Unlike the vast majority of gastropods, the shells of species of Cirsotrema (and of some other epitoniids) are calcitic, and are therefore often preserved in faunules from which aragonitic species have been removed by diagenesis, such as in limestones.

Distribution: Whaingaroan-Duntroonian, ?Waitakian; Aotea Harbour, Southwest Auckland, Duntroonian ? (type locality of both S. lyrata and S. browni); possibly much longer-ranging.

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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