Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 8r): GS9508, J40/f8803, McCulloch's Bridge, Kaiatan (GNS)
Beu & Maxwell (1990): Chapter 8; p. 126; pl. 8 r.
Synonymy: Turris bimarginatus Suter 1917, p. 44-45
Classification: Turridae: Turrinae
Description: Rather small for subfamily (height 12-18 mm), narrowly fusiform, spire 0.6 total height. Protoconch conical, of about 5 strongly convex whorls, last 2.5 whorls with narrow, opisthocyrt costellae, remainder smooth. Teleoconch of 6-7 whorls, spire whorls with a prominent though not greatly projecting peripheral band at or near middle; sutural ramp strongly concave, with a prominent subsutural fold; last whorl with a prominent peribasal keel, excavated below with a moderately long, narrow neck. Axial sculpture confined to peripheral band, of rounded gemmules of squarish outline, with interspaces of similar width; 13-18 on penultimate whorl. Spiral sculpture consisting of a cord on subsutural fold, 3 narrow threads of variable strength on peripheral band, and an almost submerged suprasutural cord; most shells with a few fine threads on ramp, some with an additional cord about halfway between periphery and lower suture. Suprasutural cord emerging on last whorl as peribasal keel, accompanied by a somewhat weaker one on base, and up to 18 weak cords on base and neck. Aperture elongate-pyriform, with a moderately long, unnotched siphonal canal. Inner lip impressed adapically; outer lip thin, smooth within, anal sinus deep, narrowly U-shaped, apex on peripheral band.
Comparison: The sympatric species Gemmula duplex is similar in size, but has a narrower, less strongly sculptured protoconch, a narrower peripheral band and a row of gemmules rather than a spiral cord bordering the upper suture. G. bimarginata differs from G. waihaoensis (also McCulloch's Bridge) in its smaller size and more rounded peripheral gemmules, by the absence of subsutural collabral ridges and in having two prominent basal spiral cords. These species were discussed further by Maxwell (1992, pp. 144-147).
Gemmula is first recorded from about Mangaorapan in New Zealand and seems to have become extinct in the North Otago-South Canterbury region during or after the Waitakian, although elsewhere (Clifden, Southland, and further north) it survived until the Opoitian. Recent species are widely distributed in tropical or subtropical waters, mostly at mid-shelf to bathyal depths, although a few species occur shallower than 20 m (Powell 1964, p. 243-275).
Distribution: Kaiatan; "Teaneraki" (type probably lower Waihao Valley); Waihao Greensand, McCulloch's Bridge (not uncommon).
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)