the polished disk, but slightly irregular medially. Ligament deeply sunk below the right posterior marginal groove. Pedal retractor confluent. Pallial sinus with a wide mouth and a rounded end.

Holotype in Cudmore Collection.

Length, 21.6 mm.; height, 16.8 mm.; inflation (1 valve), 6 mm.

Oligocene-Miocene: Grice's Creek, Frankston, Victoria (Balcombian).

This species is closely related to tatei (= tenuis) but differs in having persistent concentric sculpture, more deeply sunk ligament, and straighter, more steeply inclined lunular margin. In general appearance N. ancisa strongly resembles the New Zealand N. watti, differing only in having persistent sculpture across the disk.