Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 26d): GS10365, D45/f8598, Long Beach Shellbed, Clifden, Altonian (GNS)
Beu & Maxwell (1990): Chapter 11; p. 233; pl. 26 d.
Synonymy: Miomelon clifdenensis Finlay 1926b, p. 246
Type species of Metamelon Marwick, 1926
Classification: Volutidae: Zidoninae
Description: Rather small for subfamily (height 42-55 mm), elongate-ovate, spire 0.35 total height. Protoconch mamillate, of about 3 smooth whorls, with a prominent apical spike. Teleoconch of 4-5 whorls, early whorls gently convex, later whorls bluntly shouldered somewhat above mid-whorl on spire; last whorl with weak basal subangulation, slightly concave below. Axial sculpture, apart from growth lines, absent from first 2 whorls or so, later whorls with well spaced, sharp-crested costae that are noticeably thickened on shoulder angle, particularly on last whorl in some shells only peripheral nodules remain on last half-whorl; 9-13 on last whorl. Whole surface covered with numerous very fine spiral striae. Aperture elongate- ovate; siphonal notch deep, fasciole prominent, margined above by a low, sharp ridge. Columella with 5 plaits. Inner lip with a thin callus glaze; outer lip slightly thickened within.
Comparison: Specimens of Metamelon clifdenensis from higher in the Clifden section (late Lillburnian and Waiauan) have more rounded whorls than typical Altonian shells, with little or no suggestion of a shoulder. Some of them have a very inflated last whorl and so have a superficial resemblance to Lyria zelandica. Metamelon resembles Spinomelon in having an apical spike, but differs in its smaller size, and in having a deep siphonal notch and a prominent, ridge-margined fasciole. However, in view of the new appreciation of New Zealand zidonine volutes arrived at from molecular phylogeny, it seems unlikely that Metamelon is a separate genus. M. clifdenensis differs from other described species in having distinctly shouldered whorls and prominent axial costae.
Distribution: Altonian-Lillburnian; Calamity Point Sandstone, Clifden, Altonian (type); Fouraye Siltstone, Long Beach Shellbed, Slip Point Siltstone and Third Bay Sandstone, Clifden, moderately common.
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)