Obliquely oval, minute, inequilateral; umbos fairly sharp and prominent; sculpture of numerous concentric lirae crossed by radial lirae, the latter slightly closer than the concentrics, forming rectangular spaces; umbonal third of shell smooth; ventral margin denticulated internally and externally; shell colour yellowish-white, polished. Holotype, length 2.5 mm., height 2 mm., section 1 mm. Gulf St. Vincent, 15-20 fathoms.

DIAGNOSIS: A trapezoid ovate, small shell, with relatively broad radial ribs on median area of dissoconch, an anterior hinge plate which tapers towards the umbo, a rather large oblique chondrophore, a broad posterior hinge plate, and a crenulated inner ventral margin.
DESCRIPTION: Valve small, rather inflated, trapezoid ovate in outline, with the greatest height in the anterior part; delicate but not very thin. Dorsal margin slightly and evenly curved, angulations between dorsal and anterior and posterior margins marked but not sharp. Posterior margin short and slightly rounded. Anterior margin long and weakly curved. Ventral margin broadly rounded but for an almost straight posterior part, with broad curvings passing into anterior and posterior margins. Embryonic shell with microscopically pitted outer surface, interdissoconch smooth but for fine growth lines. Dissoconch with some pronounced growth lines (that do not take the shape of riblets), and with radial ribs on its median area; interstices between the ribs rather broad. Radial ribs extending farther on anterior and posterior areas than in Nucula decorosa (Hedley). Growth lines most prominent on anterior and posterior extremities. Periostracum light brown. Anterior hinge plate rather long, narrowing posteriorly, extending over chondrophore and ending just before umbo. Anterior secondary teeth up to 9, narrowing with hinge plate, with somewhat curved tips. Posterior hinge plate relatively short and broad, only narrowing between its first secondary tooth and umbo and ending posterior of umbo. Up to 3 posterior secondary teeth. Chondrophore solid, rectangular, obliquely projecting into the valve towards anterior part of ventral margin and supported by 4 or 5 ridges on the valve interior. Posterior supporting ridge strongest, running from posterior side of chondrophore towards posterior hinge plate. Posterior primary teeth consist of one rather strong tooth in right valve, opposed by two teeth in left valve. Anterior primary teeth consist of a distinct and an obtuse tooth in the right valve, opposed by what seems a thickened dorsal margin in left valve. Pallial line entire and indistinct. Adductor muscle scars distinct and oblongly ovate. Inner ventral margin crenulated by radial shell structure. Holotype Length: 2.32; Height: 1.88

Eastern South Australia