Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 25i) holotype, Hokianga South Head, Otaian (TM1273, GNS)
(Pl. 25j): GS9869, N2/f7608, Paramateha, north shore, Parengarenga Harbour, Altonian (GNS)
Beu & Maxwell (1990): Chapter 11; p. 237; pl. 25 i,j.
Synonymy: Architectonica (Discotectonica) marwicki Laws 1948, p. 149 (not of Allan, 1926); A. hokianga Vella 1954, p. 544 (new name for A. marwicki Laws, preoccupied); Discotectonica hokianga, Beu & Maxwell 1990, p. 237, pl. 25i, j
Description: Moderate-sized for genus (diameter 7-15 mm), lenticular, spire a depressed cone. Protoconch smooth, heterostrophic, with strongly immersed initial whorl. Teleoconch of 4-4.5 whorls, spire whorls gently convex; last whorl with prominent, narrowly rounded peripheral keel, base sharply contracted, gently convex with a deep, moderately wide umbilicus. Spiral sculpture of very low, flat-topped or gently convex cords with narrow interspaces, 5 on penultimate whorl, the lowest emerging on last whorl as peripheral keel, all cut up into low gemmules or flat-topped lozenges by strongly prosocline, incised growth lines. Base with a narrow rounded cord bordering the peripheral keel and a much weaker one between; a deeply incised groove bounding a broad, coarsely and irregularly crenulate circumumbilical band; space between with prominent radial ridges and weak spiral threads. Aperture ovate, inner lip vertical, with a short, horizontal channel at end of circumumbilical band.
Comparison: Discotectonica hokianga is distinguished from other New Zealand architectonicids by its depressed-lenticular shape, its relatively narrow umbilicus, and its coarsely crenulate circumumbilical band, in having low, flattened spiral cords cut into lozenges by growth lines, and in having a deeply incised groove bordering the circumumbilical band. Discotectonica seniscula (Altonian-Lillburnian, Gisborne district) is most similar, but differs in having a broad, almost smooth band between a narrow, very low subsutural band and the peripheral cord.
Discotectonica Marwick, 1931 (type species D. balcombensis (Finlay, 1927); Middle Miocene, Victoria, Australia) differs from Architectonica Roding, 1798 (type species A. perspectiva Linné, 1758; Recent, Indo-Pacific) in having a relatively low spire, in having the outer lip attached to the peripheral cord (rather than some distance above), and in lacking a prominent abapical cord margining the lower suture (on spire whorls) or the peripheral cord (on last whorl). Although usually classed as a subgenus of Architectonica, Discotectonica was given generic rank by Bieler (1985, p. 241; 1993, p. 129) who we follow here. Architectonica (sensu stricto) does not seem to have been recorded from New Zealand the Recent species A. reevei (Hanley, 1862), which occurs rarely in the northern part of the North Island, was made the type species of the new subgenus Adelphotectonica on the basis of shell and radular characters (Bieler 1987, p. 208), and Bieler (1993) recognised this as a genus.
Distribution: Otaian-Altonian; Hokianga South Head, Northland, Otaian (type); north shore, Parengarenga Harbour; ?Gisborne district.
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)