Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 49l): GS2185, R22/f6312, Tainui Shellbed, Castlecliff, Wanganui, Castlecliffian (GNS)
Beu & Maxwell (1990): Chapter 16; p. 368; pl. 49 l.
Synonymy: Pleurotoma buchanani Hutton 1873b, p. 4; Drillia buchanani; Pleurotoma (Drillia ?) maorum E.A. Smith 1877, p. 497; Antimelatoma ahiparana Powell 1942, p. 98; Antimelatoma benthicola Powell 1942, p. 98.
Type species (as "Drllia maorum" Smith) of Antimelatoma Powell, 1942
Classification: Conidae: Clathurellinae(?) (not analysed by Puillandre et al. 2008)
Description: Moderate-sized for family (21-25 mm high), tall and narrow, with moderately tall, stepped spire (slightly taller than aperture and canal), long, straight, open, unnotched anterior canal without fasciole, a prominent but narrow, smooth subsutural fold, and a strongly concave sutural ramp. Whorls prominently shouldered by abrupt initiation of axial costae at base of sutural ramp (i.e., base of anal sinus), otherwise gently and evenly inflated on spire; gradually and gently tapered over base to narrow canal. Sculpture of many narrow, well raised, closely spaced spiral cords, 5-8 on spire whorls and about 18 on last whorl, with several fine spiral threads in each interspace on spire and upper part of last whorl; crossing (with only very small, rounded nodules) long, rounded, closely spaced axial costae, about 15 per whorl, prominent on spire but becoming less so on last whorl. Aperture simple, with thin lips, no parietal callus or stromboid notch; anal sinus wide, moderately deep U-shaped, occupying sutural ramp. Protoconch dome-shaped, of slightly more than 2 whorls; first whorl smooth, the second with 4 spiral cords.
Comparison: The Haweran and living form named Pleurotoma (Drillia?) maorum by Smith (1877) differs from A. buchanani only in having the uppermost cord around the shoulder and the second one below it raised above their neighbours, and even Powell (1942, p. 97) realised that the fossil and living populations are both highly variable in sculpture, and that A. maorum may not be separable from A. buchanani. Comparison of specimens from thoughout New Zealand showed that all named forms intergrade, and only a single species was recognised by Beu (2009). Specimens from Landguard Sand (Haweran, oxygen isotope stage 9) at Wanganui have fewer, more prominent spiral cords than most Recent shells, and are identical to the form named A. ahiparana by Powell (1942). However, this intergrades clinally along the western North Island at present with A. buchanani, and Landguard Sand specimens are merely normal western specimens. Beu (2009) named an apparently ancestral species with coarser sculpture from Kapitean and Opoitian rocks in Westland, putting the apparent arrival of the genus in New Zealand back to Late Miocene time.
Distribution: Nukumaruan-Recent; "Shakespeare Cliff", Wanganui [Tainui Shellbed ?], Castlecliffian (type); common in all siltstone beds in the Castlecliff section, Wanganui, and in Nukumaruan siltstone in Hawke's Bay, Wairarapa and North Canterbury; Recent, on the continental shelf and in the upper bathyal zone throughout New Zealand. Fossils are syntopic with Aoteadrillia wanganuiensis at most localities, but less common.
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)