Diloma zelandica: As Monodonta atrovirens, Philippi, 1851.
Shell orbiculate-conoidal, solid, imperforate, greenish-black. Sculpture consisting of spiral narrow sulci, 7 to 9 on the penultimate whorl, the flat cinguli crossed by close and fine lines of growth; base with about 7 sulci, a little closer together: Colour greenish-black, very often with irregularly scattered yellowish dots. Epidermis shining, often eroded on the spire, but seldom rubbed off. Spire depressed conoidal, sides very convex, apex sharp. Protoconch conic, small, of 2J smooth whorls. Whorls 6, rapidly increasing, slightly convex and depressed above, last whorl rounded at the periphery ; base flatly convex. Suture impressed, margined below by a cingula much broader than the succeeding ones. Aperture subrhomboidal, pearly and lirate within. Outer lip convex, sharp, black-edged, then a broad silvery band, often followed by a broad white and opaque callosity. Columella oblique, nearly straight, nodulous at the base, the callus extending on the inner side of the basal lip. Inner lip broadly expanded, bounded by green or blackish-green ; a distinct tongue-shaped pit at the centre of the umbilical tract, extending downward to the basal lip.
Diameter, 14-23 mm. ; height, 9-17 mm.
Hab.—Tasman Bay (type) ; Hauraki Gulf (II. S.) ; west coast of the North Island ; Lyall Bay (H. S.) ; Te Onepoto, near Lyttelton (H. S.) ; St. Clair, near Dunedin (H. S.).