Thyasira equalis

(Verrill & Bush, 1898)

Along the postero-dorsal margin this shell has a slightly sunken, lanceolate portion clearly marked off by an incised line. The radiating undulation on the posterior part is broad and shallow. The hinge margin is essentially the same in both valves, the vestige of a cardinal tooth is lacking (noticeable in Thyasira gouldi ). Also, in comparison with T. gouldi , the hinge-margin is thinner. In larger specimens the height of the shell most often exceeds the length, the outline being somewhat pyriform. In some specimens, however, length and height are about equal and the outline more evenly rounded.

Up to 5 mm.

Dark brown or black incrustations at the margins in front of and behind the umbo are common.

The thickened margin of the mantle is open all round and not prolonged into siphons. The long slender foot is almost cylindrical.

From 10-15 m down to 2810 m. Mainly obtained from depths exceeding 100 metres. On loose or tough clay with or without a content of coarser components.

Probably panarctic and abyssal (Distr. T. equalis).