Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 5f): GS9959, J40/f6610, South Branch, Waihao River near "Pentland Hills", Bortonian) (GNS)
(Pl. 5i): GS9959, J40/f6610, South Branch, Waihao River near "Pentland Hills", Bortonian) (GNS)
Beu & Maxwell (1990): Chapter 7; p. 101; pl. 5 f, i.
Synonymy: Astarte australis Hutton 1873b, p. 25; Spissatella australis; Crassatellites tripliciter Laws 1935b, p. 23
Description: Moderately large for family (length 50-80 mm), robust, subtrigonal; dorsal margins steeply descending, almost straight, anterior and ventral margins convex, posterior margin rounded-truncate. Umbonal ridge rounded, more strongly defined proximally than distally, demarcating a relatively narrow, somewhat flattened or slightly concave posterior area. Lunule and escutcheon prominent, strongly impressed. Commarginal sculpture of low, rounded costae on umbones, extending up to 15 mm or so from beaks, remainder of shell with growth lines and grooves. Some individuals with weak radial costellae near ventral margin, otherwise devoid of radial sculpture. Hinge plate prominent, triangular; left valve with narrow, transversely grooved, anterior cardinal tooth separated from lunule by shallow groove, an equally narrow median cardinal tooth and a short, low posterior cardinal tooth that barely diverges from escutcheonal margin; posterior lateral tooth a low ridge on ventral edge of hinge plate, separated from escutcheonal margin by broad, shallow groove which accommodates right escutcheonal margin. Right valve with narrow anterior cardinal tooth largely fused to lunular margin, and a prominent though narrow median cardinal tooth; anterior lateral a low short swelling on ventral margin of hinge plate with a shallow socket above to take distal end of left lunule. Resilifer large, triangular, not extending to ventral margin of hinge plate. Adductor muscle scars subequal, strongly impressed; pedal retractor scar subcircular, strongly impressed, on underside of anterior end of hinge plate. Ventral shell margins smooth or finely crenulate.
Comparison: Eucrassatella australis differs from E. ampla (Pl. 12d, e) in its much smaller size, its more equilateral, subtrigonal shape and in the presence of marginal crenulations in some individuals. Some specimens of E. marshalli (Kapitean-Waipipian) approach E. australis in shape, but they differ in having a smaller, less well-defined lunule, a much wider and deeper groove separating the left anterior cardinal from the lunule, a resilifer that extends to the ventral margin of the hinge plate, and in lacking marginal crenulations entirely. E. australis has long been assigned to Spissatella Finlay, 1926, but it is closer in size, shape and sculptural characters to typical species of Eucrassatella. Large specimens of E. australis are characteristic of shallow-water (inner or middle shelf) assemblages; small shells (less than 20 mm long) occur in deeper-water facies (e.g. at McCulloch's Bridge).
Distribution: Mangaorapan?; Porangan?; Bortonian-Kaiatan; Waihao Greensand, Kakahu, Bortonian (type locality of A. australis); Waihao Downs, Bortonian (type locality of C. tripliciter); South Branch, Waihao River near "Pentland Hills"; Otaio Gorge; McCulloch's Bridge. Not uncommon in shallow-water, sandy bottom assemblages.
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)