Shell minute, thin, semitransparent, dull-white, inflated, globular. Prodissoconch large, central, projecting, marked off by a rim; anterior and posterior knobs present but not prominent. Surface smooth. Valve margins smooth above but weakly crenulated ventrally by a few very feeble radial folds which are confined to the lower third of the shell. Hinge typical, three cardinals in the left valve and two in the right. 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 slender cardinal thickened at the proximal end, followed by a slight groove for the reception of the posterior cardinal in the right valve. After the resilium there is a short thickened clasping cardinal, followed by a socket, a long cardinal and finally the marginal space for the anterior thickened margin of the right valve. In the right valve there is first the slight thickening of the margin above, followed by a long socket and an equally long cardinal, then resilium, followed by an obscured groove occupied by the short clasping cardinal of the left valve; this is followed by a moderately long flexuous lamellate cardinal, then a socket and finally the slight anterior thickening of the valve edge.
Length, 0.98 mm.; height, 0.98 mm. (Holotype).
Length, 1.06 mm.; height, 1.04 mm.; thickness (two valves) 0.67 mm. (Paratype).
Holotype presented to Auckland Museum.
Habitat, Mangonui Heads in 6-10 fathoms (type). (Mr. "W. La Roche, 1922); Awanui or Rangaunu Bay in 12 fathoms. (Mr. "W. La Roche, 1922) ; 38 fathoms off Cuvier Island (Dr. H. J. Finlay); Castlecliff, Upper Pliocene (Dr. H. J. Finlay). The writer is indebted to Dr. H. J. Finlay for the opportunity for examining the Cuvier Island and Castlecliff specimens.