Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 2b): GS10195, I44/f8486, Boulder Hill, Wangaloan (GNS)
Beu & Maxwell (1990): Chapter 5; p. 80; pl. 2 b.
Synonymy: Turritella semiconcava Suter 1911, p. 595
Type species of Leptocolpus Finlay & Marwick, 1937
Description: Moderately large for family (height 70-90 mm), attenuate. Protoconch not known. Early teleoconch whorls sharply angled medially by spiral B, A and C remaining very weak until about 5th whorl when A increases in strength, B shifts to a more abapical position, secondary spirals appear and whorls become biangulate. During growth B decreases in dominance, C and secondaries increase in strength and whorls become flat-sided or gently concave. Adult whorls with about 9 subequal cords and a few weaker ones, particularly adapically. Base with about 10 additional spirals, those at and just below periphery stronger than those below. Outer lip with broadly arcuate, rather shallow sinus, both limbs almost straight, the adapical limb extending further forward than the abapical one.
Comparison: Zeacolpus semiconcavus is one of the most common molluscs at Wangaloa, Boulder Hill and Waihao River. It is distinguished from superficially similar, younger species of Zeacolpus (e.g. Z. pukeuriensis, PI. 20a) by its much shallower outer lip sinus with a markedly less strongly opisthocline abapical limb. Z. semiconcavus is the oldest known member of the genus, and its relationship to the deeper-sinused species (which are first recorded from beds of probable Early Eocene age in the upper Waihao River) is uncertain.
Distribution: Wangaloan, Wangaloa Formation, Wangaloa (type); Boulder Hill; Kakanui valley; lower Waihao River; Castle Hill Basin.
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)