Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
| | Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990) |
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  (Pl. 16a): GS958, J41/f8497, Old Rifle Butts, Cape Wanbrow, Oamaru, Altonian (GNS) |
 (Pl. 16c): GS958, J41/f8497, Old Rifle Butts, Cape Wanbrow, Oamaru, Altonian (GNS) |
Beu & Maxwell (1990): Chapter 11; p. 176; pl. 16 a,c.
Synonymy: Neilo awamoana Finlay 1926b, p. 233
Classification: Malletiidae
Description: Size moderate for genus (length 25-35 mm), subrectangular; anterior end rounded, posterior end truncate, slightly sinuous; postero-umbonal ridge well-defined, posterior area with 2 very weak radial subangulations producing a shallow sulcus. Lunule narrow, depressed; escutcheon very well defined, bounded by a sharp ridge. Commarginal sculpture prominent, variable, of narrow, rather sharp ridges, of similar strength on posterior area as on flanks, but not extending onto lunule or escutcheon; c. 2.2 per mm centrally. Hinge prominent, anterior series with 18-24, posterior series with 27-30 chevron-sectioned teeth. No resilifer, but a shallow embayment for external ligament extending back from hinge rather less than half length of posterior part of hinge. Adductor muscle scars subequal; pallial sinus short, rounded.
Comparison: Neilo sinangula (Duntroonian, Wharekuri) is very similar to N. awamoana and was classed as a subspecies of the latter by Marshall (1978, p. 430-431). The only important difference between the two taxa is that commarginal sculpture tends to be considerably weaker on the posterior area (particularly distally) than on the flanks in Wharekuri shells, but similar in strength over the entire shell in typical N. awamoana. In this respect specimens of Neilo from Brother's Stream and Sister's Creek, Hakataramea Valley (Waitakian) are more similar to Wharekuri shells than to younger specimens and are therefore assigned to N. sinangula. Finlay (1926b, p. 255) claimed that N. awamoana was ancestral to the Nukumaruan-Recent N. australis, but Marshall (1978) concluded that it was probably the ancestor of N. wairoana (Nukumaruan) and its Recent subspecies N. wairoana delli Marshall, 1978. The latter taxon is confined to the upper bathyal zone, but N. awamoana seems to have extended into considerably shallower, probably mid-shelf depths.
Distribution: Otaian-Altonian; Mount Harris Formation, Mt Harris, Otaian-Altonian (type); Bluecliffs, Otaio River; Awamoa Creek and other Altonian localities in Oamaru district. Common at most localities, particularly in off-shore siltstone facies.
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
ISBN
978-0-478-19705-1
ISSN 1177-2441
(Included with a PDF facsimile file
copy of New Zealand Geological Survey Paleontological Bulletin 58 in CD version
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