Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 41g): GS1164, R22/f6438, Tewkesbury Formation, Nukumaru Beach, west of Wanganui, Nukumaruan (GNS)
(Pl. 41j): GS1164, R22/f6438, Tewkesbury Formation, Nukumaru Beach, west of Wanganui, Nukumaruan (GNS)
Beu & Maxwell (1990): Chapter 15; p. 316; pl. 41 g,j.
Synonymy: Venus sulcata Hutton 1887, p. 226 (in part only); Chione subsulcata Suter 1905b, p. 205; Cytherea subsulcata
Classification: Veneridae: Venerinae
Description: Large for genus (30-35 mm long), weakly trigonal in outline (with only lightly convex antero-dorsal and postero-dorsal margins), moderately inflated. Sculpture of many coarse, prominent, commarginal ridges, 7- 8 per cm near ventral margin, narrower and weakly anastomosing near anterior and posterior ends; each ridge concave dorsally and strongly convex ventrally in cross-section, crossed by very fine radial threads, and (an unusual character for Tawera) separated from neighbouring ridge by a gap about half the width of 1 costa. Lunule narrow, slightly concave, marked off by deep groove. Interior of ventral margin finely crenulate. Hinge moderately deep, with 3 narrow cardinal teeth in each valve, median one deeply grooved in left valve, and both posterior and median ones grooved in right valve. Adductor scars large, oval. Pallial sinus short and very narrow.
Comparison: Tawera subsulcata (as used at present, assuming the lectotype comes from Nukumaru) is a little taller and considerably larger, thicker, and more coarsely sculptured than the common near-shore, Castlecliffian and living, mainland species T. spissa, but not as tall or nearly circular as the southern living species T. marionae Finlay and T. bollonsi Powell. The Hawke's Bay Nukumaruan species T. assimilis is longer and lower than T. subsulcata, whereas the Chatham Islands Nukumaruan species T. marthae is considerably larger but more finely sculptured than T. subsulcata. Really typical T. subsulcata (with spaces between the commarginal ridges) occurs only in Nukumaru Limestone, Nukumaru Brown Sand, and Tewkesbury Formation at Nukumaru Beach, west of Wanganui (Nukumaruan), but similar shells occur in the Nukumaruan of Wairarapa and North Canterbury and in many Haweran terrace faunas around Wanganui, in Cook Strait, and around the eastern South Island, always in extremely shallow-water, soft-bottom facies.
Distribution: Nukumaruan (-Haweran?). Nukumaru Beach, west of Wanganui (presumably from either Nukumaru Brown Sand or Tewkesbury Formation), Nukumaruan, lectotype of Chione subsulcata; Marwick (1927, p. 616) identified this specimen as a "neotype" in the text, but as a "lectotype" in the figure caption; the specimen cannot be found in GNS (Keyes 1972, p. 81) and its status is in doubt. Suter (1905b, p. 205) stated that his name Chione subsulcata was a new name for Venus sulcata Hutton of Pliocene usage (i.e., not the much larger "Miocene" taxon Hutton also included under this name, = Atamarcia benhami). However, Suter's action constitutes proposal of a new species, and as Suter did not select a holotype, all the specimens he had before him must be construed as syntypes. As the lectotype(?) selected by Marwick (1927) is lost, a new lectotype should be selected from remaining Suter syntypes, if any can be identified positively. As the taxonomy of Tawera is subtle and poorly understood, care is needed to be sure the name is conserved in its present usage.
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)