Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
| | Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990) |
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  (Pl. 15l): GS9806, F45/f9668, Shell Gully, Chatton, Duntroonian (GNS) |
Beu & Maxwell (1990): Chapter 10; p. 163; pl. 15 l.
Synonymy: Trigonostoma christiei Finlay 1924b, p. 466-467
Classification: Cancellariidae: Cancellariinae
Description: Moderately large for family (height 40-53 mm), elongate-ovate, spire narrowly pointed, half total height. Protoconch mamillate of 2.5 strongly convex whorls, smooth except for weak spiral threads on last half-whorl. Teleoconch of 6-7 whorls, convex at first, soon developing a narrow horizontal shelf with its outer edge coronated by axial costae, shelf becoming channelled on later whorls on some shells; sides subvertical, slightly convex; last whorl convex, anterior end narrow. Axial sculpture of prominent, rounded, prosocline costae, reaching from suture to suture on early whorls but weakening considerably or even becoming obsolete on sutural shelf and becoming more widely and more irregularly spaced on later whorls; extending across base to fasciole on last whorl, and continuing, though much reduced, into pseudumbilicus; 13-15 costae on penultimate whorl. Spiral sculpture very weak or obsolete on sutural shelf; below shoulder consisting of low rounded or somewhat flattened prominent cords, each pair typically with a narrower interstitial cord and in some cases, threads as well; 4 or 5 primary cords on penultimate whorl and 7 or 8 additional ones on base of last whorl. Spirals crossing axial costae unchanged. Aperture ovate-trigonal, with a shallow anterior spout; columella inclined somewhat to right, bearing 2 prominent plaits and in some shells, a much weaker one anterior to them. Inner lip thickly callused in adult shells, outer edge detached in some specimens, smooth except for a few weak tubercles or ridges near anterior end. Outer lip almost straight, prosocline, smooth within. Fasciole prominent, convex, forming a small pseudumbilicus between it and inner lip.
Comparison: Scalptia (?) christiei is one of the largest New Zealand cancellariids, rivalled in size only by Maorivetia brevirostris (Pl. 22f). Although long included in Trigonostoma Blainville, 1827, it differs markedly from the type species, T. scalare (Gmelin, 1791) (Recent, Indo- Pacific), which has loosely coiled, almost disjunct teleoconch whorls, a very broad sutural shelf, a triangular aperture, and a true umbilicus. Finlay (1924b, p. 466) originally assigned T. christiei and the closely similar T. waikaiaensis Finlay, 1924 to the "section" Ventrilia Jousseaume, 1887 but the species assigned to that taxon (based on the Recent Caribbean V. ventrilia Jousseaume, 1887, = Cancellaria tenera Philippi, 1848) share most of the important diagnostic characters of Trigonostoma. T. christiei and T. waikaiaensis are here referred somewhat doubtfully to Scalptia Jousseaume, 1887, which differs from Trigonostoma in having three rather than only two columellar plaits. Species referred to Scalptia further differ from Trigonostoma in being more narrowly umbilicate, or pseudumbilicate or even non-umbilicate. S. christiei differs from typical Scalptia species in its much larger size, in having a weak third plait (obsolete in some large shells) and in lacking internal lirae on the outer lip. The Australian genus(?) Sydaphera Iredale, 1929 is another possible position, but it is uncertain whether this is separable from Scalptia.
Scalptia waikaiaensis was described on the basis of three specimens from Muddy Terrace, Waikaia, Southland, from a horizon of about the same age (Duntroonian) as S. christiei but no longer accessible. According to Finlay (1924b, p. 466) it differs from S. christiei in its smaller size and in having less strongly staged whorls and fewer axial costae, but more material is required before it can be determined if it is really a distinct species.
Distribution: Duntroonian, Chatton Formation, Shell Gully, Chatton (type), 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
ISBN
978-0-478-19705-1
ISSN 1177-2441
(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)