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Notocallista (Fossacallista) tersa n.sp. Plate 14, figs. 4, 7.
Shell rather small, more elongate oval than parki and nearer the shape of tecta, from which it differs in being more acuminate posteriorly. Sculpture of fine concentric grooves about the strength of tecta but very irregular, obsolete medially. Lunular margin slightly concave, intermediate between tecta and parki. Hinge with a very small right posterior cardinal and with the left posterior cardinal coalescing with the nymph. Pedal retractor confluent with the adductor, the junction somewhat restricted. Pallial sinus roundly truncated.
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Holotype in Auckland Museum (ex Finlay Collection).
Length, 20 mm.; height, 13 mm.; inflation (1 valve), 4.8 mm.
Locality: Shell bed, Target Gully, Oamaru.
A single specimen 29 mm. long in the Geological Survey Collection, from Target Gully, has coarse sculpture and rather straight lunular margin like parki, but the long shape of tersa and tecta. Its pallial sinus is rounded in front. Judged by its colour it probably came from the glauconitic sandstone underlying the shell-bed. N. parki occurs in this bed and the specimen may represent a transition or a hybrid between parki and tersa, with which it can be classed because of its shape.