Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 7a): GS9481, J41/f8025, Lorne, Kaiatan (GNS)
(Pl. 7b): GS9481, J41/f8025, Lorne, Kaiatan (GNS)
Beu & Maxwell (1990): Chapter 8; p. 114; pl. 7 a, b.
Synonymy: Fossularca januaria Marwick 1926b, p. 310-311; Arcopsis januaria
Description: Rather small for family (length 7-18 mm), subrectangular, strongly inflated, posterior area not clearly differentiated. Sculpture highly discrepant, left valve with about 35 narrow, beaded costellae, interspaces with finer, beaded secondary (and even tertiary) costellae crossed by numerous fine growth lines and, at irregular intervals, interrupted by much stronger growth ridges. Right valve with fine, low, closely spaced commarginal ridges crossed by very numerous radial costellae, apparently forming minute tubercles at intersections, but appearing almost smooth in some shells because of abrasion. Cardinal area long, narrow, with a shallow, triangular, vertically striate ligament pit below beaks. Hinge teeth short, appearing to radiate from near middle of shell, extending most of length of hinge. Margins smooth.
Comparison: Quadrilatera januaria is readily distinguished from other New Zealand arcoid bivalves by its small size, its rounded ends, its discrepant sculpture, its small, triangular ligament pit and its smooth internal margins. This is the only New Zealand species of this typically warm-water genus and of the Family Noetiidae to have been described to date, but other species are known from the Early Eocene of North and South Canterbury.
Arcoids of this type have long been referred to either Fossularca Cossmann, 1887 or to Arcopsis Koenen, 1885, but Ward and Blackwelder (1987, p. 136) drew attention to Deshayes' (1860, in 1856-1860, p. 866) much earlier but hitherto overlooked name Quadrilatera for this group. Neave (1940, p. 1) cited Sandberger, 1863 as the author of Quadrilatera, as did Vokes (1980, p. 18) who suggested that it is possibly a synonym of Fossularca and should probably be regarded as a "nomen oblitum". Nomina oblita, i.e. forgotten names, exist again under the 1999 International Code of Zoological Nomenclature, Article 23.9, "Reversal of precedence", but the usage of Quadrilatera as an available name by Ward & Blackwelder (1987) and Beu & Maxwell (1990) rules out its recognition as a nomen oblitum and the protection of Fossularca as a nomen protectum under Article 23.9.
Distribution: Kaiatan-Whaingaroan; Kaiatan (?), Waiareka Volcanic Formation, Lorne (type); Trig M, Totara; Bridge Point, Kakanui; Deborah Volcanic Formation, Gee's Point, Kakanui. Rare at Gee's Point, moderately common at other 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)