Shell small, rotund, maximum length 4.6mm, white, with numerous, fine, comarginal striations; umbo large, anterior and inturned; lunule triangular, with fine incised margin; posterodorsal margin long and narrowly convex, meets posterior margin in smooth curve, anteroventral margin somewhat flattened, producing characteristic subangulate ventral outline, an-terior margin smoothly rounded; hinge plate narrow, teeth elongate, cardinal 1 ventrally curved and elongate, cardinals 3a and 3b particularly elongate, 3a merges with 3b and clearly separate from it; left cardinals also elongate, cardinals 2a and 2b slender and socket outlined by 2a relatively shallow, cardinal 4 elongate and not particularly pronounced; ligament external, short and opisthodetic. Mantle margin relatively broad with 3 folds, inhalant and exhalant apertures separated by fusion of inner muscular folds; lateral to inhalant aperture and close to point of fusion separating it from extensive pedal gape a pair of short papillalike tentacles derive from middle sensory folds; four lateral pairs of papillalike tentacles and one unpaired tentacle at dorsal limit of aperture; exhalant siphon short, inturned in preserved specimens, derived from inner muscular folds; no siphonal embayment; adductor muscles relatively small, anterior muscle particularly elongate; both demibranchs present, outer are much shorter than inner with ascending lamella extending dorsally to line of posterior section of hind gut; inner demibranch extensive covering viscera and foot in preserved specimens, ventral margins touch (possibly with interlocking cilia when live) (see below, p. 208); palps small and simple, with two or three ill-defined ridges on posterior pair; course of alimentary canal simple, oesophagus joins the anterior face of stomach, style sac and mid gut combined, hind gut first lies postero-dorsal to stomach before turning posteriorly along middorsal margin over posterior adductor to anus; faecal material in long, posterior, section of hindgut pelletized.

Appears to be restricted to lower slope and abyssal depths in the northwestern Atantic, 2800–4750 m.The samples recently taken by the R.V. Atlantis II and R.V. Chain were compared with the type material and correspond in all respects. The description of the shell by Verrill (1885) is detailed and accurate, and little needs to be added except to describe the hinge in more detail and to relate it to the recent descriptive formulae of Cox (1969).