Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 28d): holotype, GS1153, Q18/f9045, Mokau Road downstream from Mangapepeke Stream, north of Mt Messenger, North Taranaki, "from the Tongaporutu beds" (Marwick 1931, p. 66), Tongaporutuan (TM4183, GNS)
Beu & Maxwell (1990): Chapter 13; p. 255; pl. 28 d.
Synonymy: Modiolus altijugatus Marwick 1931, p. 66; Xenostrobus altijugatus, Beu & Maxwell 1990, p. 255, pl. 28d.
Classification: Mytilidae: Modiolinae
Description: Large for genus (60-68 mm long), with prominent, narrowly rounded umbones projecting well above dorsal margin, and situated almost at anterior end; dorsal margin long and straight, then curving strongly around to equally long, straight posterior margin; postero-ventral margin narrowly rounded; antero-ventral margin shallowly concave. Very prominent, narrow umbonal ridge widens down shell; shell surface shallowly concave above and below ridge, forming wide posterior "wing". Surface smooth and highly polished, with weak growth ridges. Interior not seen (all specimens articulated).
Comparison: Marwick understandably referred Limnoperna altijugata to the ubiquitous genus Modiolus, but Wilson's (1967) demonstration of the distinctive anatomy of the strongly ridged modern species he assigned to Xenostrobus, his assignment of the large Plio-Pleistocene species L. huttoni (Pl. 39b) to Xenostrobus, and the similarity in shape of L. altijugata to L. huttoni suggested to Beu & Maxwell (1990) that a position in Xenostrobus is more reasonable than one in Modiolus for L. altijugata; the position must always be tentative because of the lack of knowledge of the anatomy of the extinct L. altijugata. Huge specimens (to 120 mm long) from the mouth of Upton Brook, Awatere Valley (Opoitian) are similar to L. altijugata but are less strongly curved; they appear to be intermediate between L. altijugata and L. huttoni. Subsequently, Beu (2006) showed that Limnoperna Rochebrune, 1882 is an earlier name for Xenostrobus, following the demonstration by Morton (1973, 1975) that the type species, L. fortunei (Dunker, 1857) (fresh water, tropical Southeast Asia) has the same distinctive anatomy as species assigned to Xenostrobus by Wilson (1967).
Distribution: Tongaporutuan-Opoitian; Mokau Road, North Taranaki, Tongaporutuan (type), from a shallow-water "Hurupi facies" faunule that includes Amalda (Alocospira) subhebera and Marama hurupiensis; uncommon but widespread in North Taranaki, Gisborne district, Wairarapa, Marlborough, North Canterbury, and Campbell Island, in shallow-water shellbeds with diverse Mollusca.
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)