Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 7l): GS9508, J40/f8803, McCulloch's Bridge, Kaiatan (GNS)
Beu & Maxwell (1990): Chapter 8; p. 116; pl. 7 l.
Synonymy: Turritella waihaoensis Marwick 1924e, p. 328
Type species of Spirocolpus Finlay, 1926
Description: Size moderate for family (height 25-35 mm), turriculate, spire moderately elevated. Protoconch small, narrowly conical, of about 3 smooth, convex whorls. Teleoconch of up to at least 14 whorls, early ones flat-sided or gently convex, later whorls becoming biangulate because of development of strong keels. Base of last whorl almost flat, peribasal angle only weakly marked by spiral cord. Primary cord C starting at beginning of teleoconch, B appearing almost immediately after; A appearing after 2 or 3 whorls. B and C subequal for a short time, A remaining weak, but A and C becoming dominant and similar in strength while B scarcely increases. D rather weak. Secondary spiral sculpture highly variable, almost completely absent from some shells (which consequently have a polished appearance), consisting of numerous fine threads in others. A few weak spirals on base. B finely beaded on early whorls of some shells, beading only exceptionally persisting onto adult whorls. Aperture quadrate, outer lip with deep tongue- shaped sinus, its apex above middle of whorl, abapical limb steeper than adapical limb, otherwise almost symmetrical.
Comparison: Spirocolpus possibly S. waihaoensis is locally very abundant in Kaiata Formation mudstone in the Reefton and Murchison Basins on the west coast of the South Island. Spirocolpus tophinus (Kaiatan-Duntroonian) is very similar to S. waihaoensis, apparently differing only in having spiral B much weaker (obsolete in most shells) and secondary spiral sculpture consistently almost completely absent. These differences are very slight and the two "species" are probably not worth separating. S. rudis (Bortonian, Hampden) has highly variable sculpture but in many specimens spiral cord A is much weaker than B and C and all primary cords are distinctly beaded on early whorls and in a few specimens, even on the later whorls. In addition, S. rudis seems to have been much smaller than S. waihaoensis, the largest specimens seen being only 25 mm or so in height. The poorly known S. carsoni (late Dannevirke Series?) has three prominent, narrow, beaded keels throughout growth.
Spirocolpus ranges from at least late Dannevirke Series to Waitakian in New Zealand, and is represented in the Late Eocene of South Australia by S. aldingae (Tate, 1882). The main diagnostic character of the genus is the deep, almost symmetrical sinus; the Australian genus Colpospira Donald, 1900 has a similarly deep sinus but the early development of spiral sculpture is different from that of Spirocolpus.
Distribution: Bortonian-Kaiatan; Waihao Greensand, McCulloch's Bridge, Kaiatan (type); Kakahu; Waihao Downs; Pareora River. Abundant at McCulloch's Bridge, uncommon at other listed 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)