Shell brownish black, turreted, many-whorled. Whorls somewhat rounded, ornamented with numerous spiral cords and broad, distant, longitudinal costae. Sutures deeply impressed. Aperture ovate, terminating in a very short canal; outer lip sharp, denticulated by the spiral sculpture; interior dark brown, grooved. Size: 1,5 inches.

As Cerithidea alternata:
Shell moderately large, turriculated, rather solid, costate, and spirally grooved. Sculpture consisting of distant broad and rounded axial ribs, 8 to 9 on the last whorl, cut up into broad and narrow nodules by the spiral grooves, which are deep and having a small ridge in the bottom of each ; there are about 10 of these grooves on the last whorl, 2 on the periphery of the base having 2 small ridges. Colour yellowish-brown. Spire elevated conical, twice the height of the aperture ; outlines straight. Protoconch eroded. Whorls about.11, regularly and rather slowly increasing, slightly rounded ; base flat, oblique. Suture impressed, margined above, wavy below. Aperture oblique, ovate, channelled above, produced at the base into a very short oblique and truncated canal. Interior white. Outer lip convex, thickened but sharp, denticulated outside by the spiral sculpture, grooved inside, each groove corresponding with an outer spiral riblet. Columella vertical, excavated, truncated below. Inner lip sharply limited outside the columella, united with the outer lip over the parietal wall. Operculum unknown.
Diameter, 10 mm. ; height, 24,5 mm. (type). Angle of spire, 23°.
Animal unknown.
Type in the Dominion Museum, Wellington. Hab.—Tauranga (type).

These molluscs are quite common, inhabiting estuaries of rivers, mangrove-swamps and mud-flats near the sea. In the present species the colour is fairly constant, but as regards sculpture is subject to considerable variation, some examples being more strongly costate. The genus is represented in Victoria by one species and should be easily recognized.

It possesses a wide distribution, with records from South Australia, New South Wales, Queensland Victoria and Tasmania.