Rissoa Invisibilis, sp. nov.
(Fig. 9.)

Shell small, sturdy, conic ovate. Colour white. whorls four. Sculpture —distant, longitudinal, sharp costea are crossed by three similar spiral ribs, which together divide the surface into nearly square compartments; at the intersections are small projections. One spiral ridge alone appears on the penultimate whorl, both it and the longitudinals vanish on the whorl above. The base is flattened, umbilicus narrow and deep. Aperture round, columella slightly sinuate, recurved over the umbilicus, lip with a heavy varix. Length 1·15, breadth ·63 mm.

One specimen from the sand of the lagoon shore.

Shape and sculpture ally this to the group including R. trajectus, Watson. The heavy lip, open pattern of ornament, and comparative breadth of the shell clearly distinguish the novelty, one of the smallest of the genus, from any known form.

Fig. 9.