Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 26a): GS10344, D45/f8483, Calamity Point Sandstone, Clifden, Altonian (GNS)
Beu & Maxwell (1990): Chapter 11; p. 233; pl. 26 a.
Synonymy: Alcithoe phymatias Finlay 1926b, p. 248; Waihaoia (Waihaoia) phymatias; Alcithoe (Lepormax) phymatias, Beu & Maxwell 1990, p. 233, pl. 26a.
Classification: Volutidae: Zidoninae
Description: Similar to A. bathgatei but less slender and growing to a larger size (height up to at least 85 mm). Protoconch like that of A. bathgatei. Early teleoconch whorls resembling those of A. bathgatei but shoulder angulation typically becoming obvious at an earlier stage of growth and becoming much more prominent on later whorls. Axial sculpture developing in much the same way as in A. bathgatei, but tubercles quickly becoming much larger and strongly projecting, those on last whorl (and on some shells on later part of penultimate whorl as well) with little or no axial extension; 8-12 on penultimate whorl. Spiral sculpture apparently much as in A. bathgatei. Subadult shells with 4 columellar plaits, most adults with 5, in some shells on a padded portion of the columella.
Comparison: Alcithoe phymatias succeeds A. bathgatei in the Clifden section, and is almost certainly its direct descendant. Most specimens from the Calamity Point Sandstone (stratigraphically intermediate between the Fouraye Siltstone and the Long Beach Shellbed) are unambiguously assignable to A. phymatias, but some subadult shells (height 45-50 mm) cannot be satisfactorily distinguished from topotypes of A. bathgatei. A few volutes from the Slip Point Siltstone (Clifdenian) in the Clifden section compare quite closely with some individuals from the Long Beach Shellbed, but most are squatter and have more strongly angled whorls. Some are biconic with very strongly projecting peripheral tubercles, and closely resemble the holotype of Alcithoe dyscrita, which was described from Slip Point. It seems that these three nominal species are members of a gradually evolving lineage akin to that described for Aethocola alpha, beta and gamma (see above), but considerably more material is needed before it can be adequately documented.
Although these species have long been included in Waihaoia (now regarded as a synonym of Spinomelon), they lack the apical spike present on the protoconch of the type species of Waihaoia (Spinomelon allani, Pl. 8p), and were referred to Alcithoe by Beu & Maxwell (1990).
Distribution: Altonian; Long Beach Shellbed, Clifden (type); Calamity Point Sandstone, Clifden; moderately common at both localities. Specimens very similar to A. phymatias occur rarely at other localities up to as young as Hurupi Stream, Palliser Bay (Tongaporutuan), so the full time range is poorly known. It is uncertain whether the younger specimens are conspcific or are a younger homeomorph that evolved from a different ancestor.
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)