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(Jones, 1857)

Description:
Carapace elongate sub-trapezoidal, greatest height well in front of midlength; dorsal and ventral margins almost straight, converging posteriorly; anterior margin broadly rounded, posterior margin truncated. Valves with coarse primary reticulation in the posterior half; in the anterior half the primary reticulation is faint but secondary reticulation is present in the form of clusters of small, rounded fossae. In addition to the subcentral tubercle, two or three others are variously developed in the posterior half: a prominent tubercle near the ventral margin, about half-way between mid-length and the posteroventral corner, may be extended anteriorly to form a short, broad murus, particularly in male specimens, while a second conspicuous tubercle near the posterodorsal corner may in some specimens be drawn out into a tapering diagonal murus extending almost to the subcentral tubercle; a third, inconspicuous tubercle may be present in the dorsal region, a little behind mid-length. Male copulatory appendage with a subtriangular distal process and a short, inconspicuous ejaculatory duct (E. concinna 3 ).

Habitat:
A sublittoral species, found at depths from 2 to 250 metres (most commonly in the deeper part of this range) on silt and sandy silt substrates.

Remarks:
The variability of the ornament in this species led Bassiouni (1965) to recognise pitted and reticulate forms which he regarded as Pleistocene and Recent subspecies; this distinction has not been supported, however, by subsequent studies (see Hazel, 1967, for further discussion).

Distribution:
It lives in northern British waters where it is at the southern limit of its distribution; its geographical range extends from Scandinavia to Spitsbergen, Iceland and northeastern N America.

Elofsonella concinna