Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 39j): GS1164, R22/f6348, Nukumaru Brown Sand, Nukumaru Beach, Wanganui, Nukumaruan (TM2903, GNS)
(Pl. 39k): GS1164, R22/f6348, Nukumaru Brown Sand, Nukumaru Beach, Wanganui, Nukumaruan (TM2903, GNS)
Beu & Maxwell (1990): Chapter 15; p. 312; pl. 39 j,k.
Synonymy: Lutraria solida Hutton 1873b, p. 19 (not L. solida Philippi, 1851); Mesodesma grandis Hutton 1873b, p. 20; Lutraria (Lutraria) solida, Beu & Maxwell 1990, p. 312, pl. 39j, k; Lutraria (Lutraria) grandis, Beu 2006, p. 252
Classification: Mactridae: Lutrariinae
Description: Large for family (110-150 mm long), elongate; umbo at anterior third; dorsal and ventral margins lightly curved, weakly diverging, ventral margin sloping slightly downwards towards posterior; anterior end gaping narrowly all around (allowing rocking of valves for burrowing), posterior end slightly truncated and widely gaping postero-dorsally. Exterior smooth apart from growth ridges and periostracal wrinkles. Hinge narrow apart from large, very thick, postero-ventrally inclined, triangular resilifer protruding down below umbo; 2 thin, narrowly separated cardinal teeth in right valve (posterior one at anterior edge of resilial pit; anterior one partly fused with short but very prominent anterior lateral tooth), single small bilobed cardinal tooth in left valve; 1 or 2 short, indistinct posterior lateral teeth in right valve, 1 in left valve; no right anterior lateral tooth. Adductor scars large. Pallial sinus wide, very deep, extending forward almost to beneath umbo.
Comparison: The Otaian-Altonian species Lutraria trapezoidalis is smaller than L. grandis, with more nearly parallel dorsal and ventral margins and more rounded ends. Beu (2006) referred L. trapezoidalis to L. (Psammophila), along with "Zenatia" vellai Beu, 1966. The extinction of the genus at the end of Nukumaruan time is a useful biostratigraphical index. However, there are no records from rocks between Altonian and Waipipian, indicating that the mainly Indo-Pacific subgenus Lutraria (Psammophila) extended its range to New Zealand twice (during Early Miocene and Nukumaruan time), and that the mainly Atlantic subgenus L. (Lutraria) reached New Zealand during mid-Pliocene time via South Africa, transported as planktotrophic larvae in the Antarctic Circumpolar Current.
Distribution: Opoitian-Nukumaruan; conglomeratic shellbeds near Greenwood's Bridge, Lower Waipara Gorge, North Canterbury, Waipipian (type of L. solida); "East Coast, Wellington", precise locality and age unknown (type of Mesodesma grandis). The two types were illustrated by Boreham (1965, pl. 18, fig. 7; pl. 19, fig. 1-4) who commented that the matrix of the holotype of M. grandis contains Zethalia (implying the large Z. coronata or Z. zelandica rather than the small Opoitian Z. russelli). Examination of the holotype (NZGS, TM2905) showed that at least 16 fragmentary Zethalia specimens, fragments of a large, smooth brachiopod (Neothyris?), barnacle plates, and a few small bivalve fragments occur in the matrix of hard, coarse, grey sand. Partial dorsal surfaces have been newly prepared on three Zethalia specimens, revealing a smooth surface with no subsutural gemmae, indicating a Nukumaruan age. We are not aware of any localities for Lutraria solida in Wairarapa district, and it seems likely that "Wellington" should be interpreted in a broad sense (remembering the publication date of 1873), and that the provenance was central Hawke's Bay.
Lutraria grandis is common in Matemateonga Formation (Opoitian) around Waiouru, common in the Waipipi Shellbeds at Waverley Beach, west of Wanganui (Waipipian), uncommon in several Mangapanian shellbeds in Wanganui basin (Makokako Shellbed, Mangapani Shellbed), and common in Nukumaru Limestone and abundant and well preserved in Nukumaru Brown Sand at Nukumaru Beach, Wanganui (Nukumaruan). It was also recorded from several Nukumaruan localities in the Rangitikei Valley by Te Punga (1953). In Hawke's Bay, it is common at a few semi-estuarine sand localities of Nukumaruan age (notably in Kikowhero Stream, Matapiro Station, north of the Ngaruroro River, the former "Shrimpton's" of early collectors, and a possible source of the holotype of Mesodesma grandis; and in the Okauawa Stream area, Kereru Road). In North Canterbury, it seems to occur only in Lower Waipara Gorge and in Middle Waipara River opposite "The Deans" (both possibly Waipipian; "The Deans" locality is probably Mangapanian).
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)