Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 27o): holotype, S27/f8507, Bell's Creek, Mangaopari Stream, southern Wairarapa, middle Tongaporutuan (TM 6796, GNS)
Beu & Maxwell (1990): Chapter 12; p. 248; pl. 27 o.
Synonymy: Vexillitra marwicki Vella 1954, p. 544; Austromitra marwicki
Description: Small for family (6.4 x 3.2 mm), glossy, with moderately tall, weakly stepped spire, spiral row of low nodules below suture (as in most Microvoluta species), and sculpture of 13 prominent, rounded axial costae per whorl. Costae extend well down onto base of last whorl, but fade out over last quarter to half whorl on most specimens. No spiral sculpture, other than subsutural nodule row. Inner lip bearing 4 low, narrow, oblique plaits, increasing in obliquity down columella. Protoconch dome-shaped, of 1.5 apparently smooth whorls.
Comparison: Microvoluta marwicki is a typical representative of a group of similar small Microvoluta species occurring in many Miocene bathyal siltstone faunules throughout New Zealand, although not known in Pliocene or younger bathyal faunules. The larger and more elongate, more weakly sculptured M. marginata occurs in Opoitian-Recent shallow-water faunules. The bathyal M. fracta (Tongaporutuan, North Taranaki) has a much shorter spire than M. marwicki, but is otherwise similar, and the bathyal M. wainuioruensis (Tongaporutuan, southern Wairarapa) has axial sculpture on early spire whorls only.
Cernohorsky (1970c) regarded Vexillitra Marwick as a disparate group, assuming some species were based on juvenile specimens of species in other genera, and divided the species between Austromitra, Conomitra and Proximitra (Parvimitra). However, comparison of the holotypes and other specimens leaves no doubt that Vexillitra species are based on adult shells, and are closely related species of Microvoluta. We regard Vexillitra as simply a synonym of Microvoluta (Maxwell 1988a, p. 55-56).
Distribution: Tongaporutuan; Bell's Creek, Mangaopari Stream (type); common at South Wairarapa bathyal siltstone localities (middle Tongaporutuan), but not known to us from elsewhere.
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)