Shell minute, thin, semitransparent, dull-white, moderately convex, equivalve; obliquely elongate-oval, anterior end greatly produced. Surface smooth. Valve margins smooth. Prodissoconch large, bounded by a raised rim and produced anteriorly and posteriorly -as projecting rounded knobs. The anterior knob is not so conspicuous as the posterior, being partly immersed in the anterior dorsal margin, which latter is broadly arcuate and very slowly descending. Posterior slope steep, sinuous, truncated, falling away suddenly a short distance behind prodissoconch. Truncated portion slightly concave, subangled on joining the broadly arcuate ventral margin. Hinge typical three cardinals in the left valve and two in the right. The posterior cardinal in the left valve however lacks the hooked proximal end which feature is well developed in pusilla and hamatadens and is present as a slight thickening in orbicula. In the left valve there is first a narrow marginal space for the reception of the posterior thickened margin of the right valve, then a moderately long and narrow simple cardinal, followed by a groove which is obscured by the overhanging nature of the cardinal. This groove is for the reception of a short clasping cardinal in the right valve. After the resilium there is a short clasping cardinal, a socket, another cardinal and finally a narrow marginal space for the reception of the anterior thickened margin of the right valve. In the right valve there is first the thickened margin followed by & socket and a clasping cardinal. After the resilium there is another obscured groove for the reception of the anterior clasping cardinal of the left valve, followed by a long cardinal, then a socket and finally the anterior
thickened margin.
Length, 1.06 mm.; height, 0.80 mm. (Holotype).
Length, 0.98 mm.; height, 0.74 mm.; thickness (two valves)
0.45 mm. (Paratype).
Holotype and paratype presented to Auckland Museum.
Habitat, Mangonui Heads in 6-10 fathoms (type). (Mr. W. La Roche. 1922) ; Tryphena Bav in 6 fathoms, Great Barrier Island (Mr. W. La Roche, i924).