Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 25g): GS3245, Q8/f9687, Pakaurangi Point, Kaipara Harbour, Otaian (GNS)
Beu & Maxwell (1990): Chapter 11; p. 227; pl. 25 g.
Synonymy: Siphonalia flexuosa Marshall 1918, p. 264-265; Austrofusus (Neocola) flexuosus, Beu & Maxwell 1990, p. 227, pl. 25g
Description: Similar to Aethocola (Neocola) alpha but somewhat taller (height 25-37 mm) and more slender. Protoconch like that of A. alpha; teleoconch of 5-6 whorls, first whorl convex, then developing a shoulder at about mid-height, shoulder sharply angled from about 3rd to 5th whorls then becoming rounded and sutural ramp becoming steeper and concave; last whorl with only a weak basal subangulation. Axial sculpture commencing as narrow costae reaching from suture to suture but soon becoming obsolete on ramp, later becoming broader and lower as shoulder becomes more rounded, then becoming obsolete for 0.2-0.5 of a whorl only to reappear as low, rather weak nodules on shoulder. No trace of basal nodules. Spiral sculpture of numerous narrow, low cords with interstitial threads and, on last whorl, threadlets as well. Basal cords clearly differentiated on some shells, barely distinguishable from other cords on other shells. Aperture similar to that of A. alpha except that the internal lirations on the outer lip are more prominent, there is a much more distinct sinus ("stromboid notch") near the anterior end of the outer lip, and the siphonal canal is longer. Fasciole margined by a thin, continuous ridge in shells less than about 30 mm in height, ridge discontinuous in larger shells as anterior ends of previous canals become more prominent.
Comparison: Aethocola (Neocola) flexuosa is easily distinguished from other species of the subgenus by the peculiar behaviour of its axial sculpture, i.e. it becomes obsolete, only to reappear after a short distance. It is probably most closely related to the unnamed Altonian Parengarenga species (see under A. beta), sharing with it its elongate shape, its relatively large size, its long siphonal canal, and its prominent "stromboid notch", but differing in its more subdued axial sculpture and less strongly differentiated basal spiral cords. The poorly known A. (Neocola) oneroaensis (Otaian, Waiheke Island) seems to have stronger axial sculpture and a more sharply twisted columella than A. flexuosa.
Distribution: Otaian-(early) Altonian; Pakaurangi Formation, Pakaurangi Point, Kaipara Harbour (type), common in Pakaurangi Member; mouth of Waioha Stream, north shore Parengarenga Harbour (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)