Art. XIV.—On Crassatellites trailli.
[Read before the Philosophical Institute of Canterbury, 7th June, 1905.]
A Specimen of this species collected by Professor James Park, F.G.S., and presented by him to the Canterbury Museum, shows a well-marked pallial sinus. It therefore cannot be kept in the genus in which I originally placed it, but appears to belong to Mactropsis of Conrad. It resembles the Mactrida in having a prosogyrous beak, but otherwise it is more like the Mesodesmidœ, in which it is usually placed. The following is a description of the species.
Crassatella trailli, Hutton, Cat. Tertiary Mollusca of New Zealand, 1873, p. 24.
Shell solid, heavy, closed at both ends, elongato-triangular, very inequilateral, produced, flattened and roundly angulate posteriorly. Anterior end rounded; posterior end obliquely truncated. Both anterior and posterior dorsal margins nearly straight; ventral margin slightly curved. Umbones slightly prosogyrous. Exterior finely and regularly concentrically ribbed; the ribs rounded, rather narrower than the grooves, becoming obsolete on the posterior flattened slope of the shell, as well as near the ventral margin. Lunule well marked, lanceolate, smooth. Margins smooth. Adductor scars
deep, about equal in size. Pallial sinus well marked, rounded. Resillifer flat and triangular, similar in both valves. Right valve with two cardinal teeth, the central one very strong and much higher than the anterior. Anterior lateral tooth obsolete; posterior lateral strong. Left valve with two cardinal teeth; the posterior lateral obsolete, the anterior well developed.
Length, 55mm.; height, 35mm.; thickness, 21mm.: depth of pallial sinus, 7 mm.
Localities.—Wharekuri, Waitaki Valley; Mount Harris; Mount Horrible; Pareora; Awamoa.