Shell small, oblong, imperforate, polished, microscopically spirally hrate, base subtruncate. Sculpture formed by close, fine, spiral grooves, visible only under a good lens, the interspaces being broader than the grooves. Colour pure-white. Spire conical, about 1,5 times the height of the aperture. Protoconch minute, smooth, globularly pointed. Whorls 5, lightly convex, the last large, occupying nearly three-fourths of the total height, slightly flattened below the suture. Suture superficial, submargined above. Aperture vertical, pyriform, truncated at the base. Outer lip strong, descending nearly straight, then turning at a narrowly rounded angle toward the straight and slightly notched basal lip. Columella concave and truncated below. Inner lip forming a strong but narrow callus on the body-whorl, broadening above, where it joins the outer lip ; on the columella it is much narrower, covering only the inner half of it. Operculum unknown.
Diameter, 1,5 mm. ; height, 3 mm.
Type, from the Pliocene, in the Canterbury Museum, Christ church.
Hab.—Near Channel Island, Hauraki Gulf, in 25 fathoms ; near Little Barrier Island, in 20 fathoms (R. H. Shakespear) ; near Cuvier Island, in 38 fathoms (Captain Bollons) ; Queen Charlotte Sound, in 16 fathoms (Captain Bollons) ; off Otago Heads, dredged (A. Hamilton) ; Purau, Lyttelton Harbour, and Lyall Bay (Iredale).
Fossil in the Pliocene

As Rissoa coulthardi
Shell imperforate, milk-white, loosely coiled, especially the last whorl, the aperture and its posterior callosity occupying exactly one-half the entire length of the shell. Protoconch minute, shining, colourless. Whorls 5, somewhat flat, extremely glossy, the body-whorl with a few longitudinal markings of pale brown ; in some specimens these stripes are transparent. Suture shallow. Base of one speci¬men (not the type) with 4 spiral lines. Aperture pear-shaped ; a heavy callus at the juncture with the body, and a partly concealed arch in the angle. Columella nearly upright, with a wrinkled twist on the outside of the pillar. Operculum unknown. (Webster.)
Diameter, 1,5 mm. ; height, 3 mm.
Animal unknown.
Type in Mr. W. H. Webster's collection.
Hab.—Orua Bay, Manukau Harbour, in 3 fat horns
I have not seen this species.