Shell variable in size and shape; northern ones (typical), tend to be small, narrow and tall, and southern ones (valentior), large, broad and low spired, but it seems impossible to recognise two distinct types on a geographical, or any other basis. Sculpture consisting of numerous crisp radial ribs, with weaker inter-mediates, that are delicately fenestrated by dense sharp concentric threads. The fasciole is in a deep narrow groove, with a deep narrow mar¬ginal sinus, and inside, both are strengthened by a callus limb. The colour varies from white to pale greenish-white. Height 7-13 mm., length 10-26 mm.

Shell ovate-conic, fragile and thin, apex oblique, recurved. Sculpture : Radiating ribs close together, granulate ; spiral ridges of growth prominent, irregular, producing with the ribs subcancellation. Colour greyish or greenish-white. Margin crenulated. Slit deeply excavated. Interior white to greenish. Length, 10 mm. ; breadth, 7 mm. ; height, 7 mm. (type). Length, 24 mm.; breadth, 19 mm.; height, 11mm. (Chatham Islands). Length, 22 mm. ; breadth, 15 mm. ; height, 13 mm. (Chatham Islands).
The animal is unknown.
Type in the Mus. Hist. Nat., Paris.
Hab.—In fairly deep water. New Brighton, in roots of Maerocystis ; Foveaux Strait, in 15 fathoms ; Port Pegasus, Stewart Island, in 18 fathoms (Captain Bollons) ; Snares and Bounty Islands, in 50 fathoms (Captain Bollons) ; Hauraki Gulf, in 25 fathoms ; Chatham Islands ; Bay of Islands.
Remarks.—This species is variable in size and shape ; the largest specimens I have seen are from the Chatham Islands, and they are fairly solid. The examples from 50 fathoms are small and very thin.
Fossil in the Miocene and Pliocene.

New Zealand: North, South, Stewart, Chatham, Snares, Auckland and Bounty Islands, shallow water to about 100 fathoms. Northern New Zealand (type).