Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 6f): GS13813, J38/f56, Raincliff Stream, South Canterbury, Bortonian (GNS)
Beu & Maxwell (1990): Chapter 7; p. 104; pl. 6 f.
Synonymy: Keilostoma malingi Marwick 1942, p. 273
Classification: Diastomatidae ?
Description: Size moderate for family (height 10-13 mm), turriculate, spire elevated. Protoconch mamillate, of about 1 smooth whorl. Teleoconch whorls 8-9, early ones convex, later ones almost straight-sided; periphery of last whorl rounded. Sculpture commencing on about 4th whorl, consisting of imbricated (or terraced) spiral ridges stepped on adapical edge, 5-7 on spire whorls, 10-11 on last whorl. No axial sculpture. Aperture constricted posteriorly, broadly and shallowly excavated anteriorly. Inner lip callused, outer lip with a broad, low, flattened varix.
Comparison: Although long placed in the Rissoidae or Rissoinidae, Keilostoma provisionally was referred to the Diastomatidae by Ponder (1985, p. 104). The genus ranges from Late Cretaceous to Oligocene and has a wide geographical distribution. K. malingi is very similar to the type species, K. turricula (Bruguière, 1792) from the Lutetian of the Paris Basin. It is the only known New Zealand gastropod with well developed terraced (or ratchet) sculpture, a character that apparently aids burrowing in soft sediments (Signor 1983).
Distribution: Bortonian, Opuha River (type); Raincliff Stream, South Canterbury (not uncommon at both localities).
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)