Dorsal and ventral margins divergent posteriorly, greatest height behind mid-length. Posterior extremity at about mid-height. Fused zone relatively narrow throughout.
Distal process of male copulatory appendage relatively broad, tapering distally, with a convex anterior margin and an S-shaped posterior margin, the concavity of which forms an approximate right-angle. Living specimens whitish, translucent, with irregular patches of reddish pigmentation.
Sublittoral, usually found on muddy substrates. In depths down to 150 metres.
This is one of the largest species in British waters; the only other comparably large, smooth species are Paradoxostoma tenuissimum in which both anterior and posterior extremities of the carapace are sharply pointed, Paracypris polita which has a strongly arched dorsal margin and the posterior extremity well below mid-height, and Macrocypris minna, which is even larger (2-3 cm long) and has the pointed posterior extremity level with the ventral margin.
It has been recorded from the British Isles and NW Europe as far north as the Lofoten Islands, and from Baffin Bay and the Hunde Islands (W Greenland).