Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 20s): GS951A, J41/f8475, Target Gully Shellbed, Oamaru, Altonian (GNS)
Beu & Maxwell (1990): Chapter 11; p. 195; pl. 20 s.
Synonymy: Pteronotus (Pterochelus) awamoanus Finlay 1930b, p. 77; Pterochelus awamoanus; Pterotyphis (Prototyphis) awamoanus, Beu & Maxwell 1990, p. 195, pl. 20s.
Classification: Muricidae: Tripterotyphinae
Description: Small for family (height 10-17 mm), fusiform, spire half total height. Protoconch mamillate, of about 1.25 smooth whorls, rounded in most specimens, but flattened on top in a few. Teleoconch whorls 5, broadly angled near middle on spire; last whorl with weaker angulation appearing out of suture or somewhat above, broadly excavated below with moderately long neck. First whorl with 5 low, lamellar varices, later whorls with 3 prominent varices, which are more or less aligned across whorls, folded into prominent, open, upwardly curved spines on ramp and into a much smaller open spine below, just above suture on spire. Other axial sculpture of small nodules on upper angulation, 3 or 4 between each pair of varices. Spiral sculpture of a low cord margining lower suture on spire, emerging on last whorl to mark the lower angulation, accompanied by another, of similar strength or weaker, on base. Aperture ovate, columella slightly concave above, bent to left below to form slightly curved, open siphonal canal. Inner lip moderately callused, slightly detached over columella. Outer lip slightly reflected, bearing 5 prominent denticles within; terminal varix thin, frilled by 4 short, open spines below the prominent shoulder spine.
Comparison: Prototyphis awamoanus is closely similar to P. eos (Hutton, 1873) (Recent, Northland) but is much smaller and has less prominent spiral sculpture and fewer variceal spines (only one other than the shoulder spine exposed on spire whorls, in contrast to two exposed on P. eos). Fossil specimens of P. eos (Castlecliffian; Pl. 48j) have an only weakly denticulate interior to the outer lip. P. allani (Waitakian-Otaian, South Canterbury) differs from P. awamoanus in its larger size and its more prominent spiral sculpture, in having the shoulder spine almost horizontal, and in having a non-denticulate outer lip. A still larger species was recorded by Maxwell (1971) from Wharekuri Greensand, head of Lake Waitaki (Duntroonian). P. tahuensis (Maxwell, 1971) (Kaiatan, McCulloch's Bridge, South Canterbury) differs from all "younger species in having a polygyrate-conical rather than a paucispiral-mammillate protoconch and in having a relatively weakly developed canal on the variceal spine" (Maxwell 1992, p. 122).
Prototyphis has a rather puzzling stratigraphic distribution. Although it seems to have been rather widespread in New Zealand though not necessarily common from at least Bortonian to Altonian, there is only one record of the subgenus (Waipipian, Waipipi) from then until the Nukumaruan. This possibly indicates that it was absent from the New Zealand region during the Middle Miocene to early Pliocene and that the late Cenozoic records result from a new dispersal to New Zealand, but it seems more likely that for some reason it underwent a severe habitat restriction (presumably to rocky environments, both intertidally and in deeper water) and its later fossil record results from the relatively good late Cenozoic preservation of rocky shore environments. Most species of the genus are restricted to New Zealand (Houart & Héros 2009, p. 473), P. angasi (Recent, eastern Australia; common near Sydney but less common further south) and P. gracilis Houart & Héros, 2009 (Recent, Fiji) being the only exceptions.
Distribution: Altonian; Target Gully Shellbed, Oamaru (type); Ardgowan Shellbed, Oamaru; Awamoa Creek (uncommon).
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)