This shell is generally large, resembling the Venus, from which it may
be distinguished by having on the front side one impressed lateral
tooth, which is sometimes obsolete; the nymphæ or callosities of the
hinge large, arched, and terminated near the apices by a cavity,
sometimes very deep.
De Blainville says that this genus is intermediary to the Cyclas and the
Venus, and contains but one living species; Lamarck makes two, though at
first he characterized eight.
Cyprina tennistria.
Cyprina Islandica.
_C. Islandica._ The Icelandic Cyprina. Pl. 9, fig. 2.
Shell thick, regular, heart-shaped, covered with dark brown epidermis;
white interior; sub-striated longitudinally; apices very strongly
recurved anteriorly, and often contiguous; hinge thick, sub-similar,
formed by three cardinal teeth but little convergent, and by one remote
posterior lateral tooth, sometimes obsolete; ligament very thick,
convex, fixed to large, arched, nymphal callosities, preceded by a
cavity more or less deep, hollowed immediately behind the summits;
muscular impressions subcircular and very distant.