Shell small, ovate, inflated. Beaks small, situated about anterior two-fifths. Anterior margin broadly rounded, posterior margin rather more narrowly rounded, ventral margin evenly curved, no true rostrum. The whole shell is sculptured with very fine, regular, broad concentric ribs. Surface covered with a thin, light brown epidermis. Hinge line narrow, interrupted below beaks, 9 teeth in the anterior, 11 in the posterior series. Interior surface smooth and shining. Length, 4,8 mm.; height, 3,6 mm.; inflation (single valve), 1,3 mm.

This species is close to N. wrighti Fleming in shape, but may be distinguished by the greater inflation and the regular concentric sculpture. From N. benthicola it may be distinguished by the regular, well-marked concentric sculpture, greater inflation, and comparatively greater height.

New Zealand. Deep Sea. Localities: CLE. Station 5, Chatham Rise, in 300 fathoms; CLE. Station 41, south-east of Pitt Island, in 330 fathoms (type); CLE. Station 52, Chatham Rise, in 260 fathoms; CLE. Station 59, Chatham Rise, in 290 fathoms.