Shell small, subcircular, inflated, only slightly longer than high, particularly in smaller specimens (100L: 97–91H: 66W), white, shell surface matt, fine microscopic comarginal sculpture except at ventral margins where rings are more marked; umbos large, anteriorly directed, incurved; antero-ventral and postero-ventral margins faintly angulate, anterior margin rounded, posterior margin with slight angulation where it meets long, curved posterodorsal margin; antero-dorsalmargin of lunule curved; lunule sunken, triangulate, lunular margin sharply incised; no escutcheon; ligament relatively long, opisthodetic, slender, barely visible externally, attached to nymphs on outer edge of posterior hinge plate; hinge plate narrow, right hinge with cardinal 1 anterior to umbo forming short V at ventral margin of plate, cardinals 3a and 3b not clearly sep-arate, form elongate, slender ridge at ventral margin of hinge plate, slightly thickened posteriorly, cardinals 1 and 3a separated by narrow groove, posterior to cardinal 3b hinge plate merges with thickened, shallowly grooved postero-dorsal margin, hinge plate of left valve with slender cardinal 2a interlocking dorsal to cardinal 1, cardinal 2b posterior to umbo at ventral margin of plate, elongate, narrow, anteriorly spoon-shaped interlocks ventral to cardinal 3b, left hinge plate merges with thickened posterodorsal shell margin and interlocks with shallow groove of other valve.

Kelliella abyssicola is distinguished from other species by the angularity of the shell margin, the finely ridged matt surface of its shell and the form of the hinge teeth. It most closely resembles Vesicomya adamsi (Smith, 1885) (see below) which was described from 4410m south of Sierra Leone (Smith, 1885) and from the Romanche Trench at 5250–5300m (Odhner, 1960). These specimens are much larger (12.7–13.9mm) than K. abyssicola described here (3mm maximum length). They are more elongate and with the ventral shell margin more evenly curved. The concentric sculpture is more pronounced. The ligament of V. adamsi is shorter than that of K. abyssicola and the hinge teeth differ in their form with only one cardinal tooth in the right valve reported by Smith (1885) though Odhner (1960) records a ‘‘median principal tooth ... slightly curved in an S-shape below the umbo, and a curved notch in its formost under half, as well as a front tooth projecting downwards below a central hole limited in front by a callus’’. This differs markedly from the hinge described above. While experience shows that shell

Lower slope and abyssal depths in the North Atlantic to the southwest of Ireland and in the Sierra Leone and Guyana Basins. Depth range 2185–4632m.