Distinguished from the Arca by the muscular impression within, to one
side of which is an ear-shaped testaceous appendage; the shell is more
trapeziform, and the hinge by age becomes obsolete, giving the teeth a
more horizontal appearance.
Shell equivalve, inequilateral, trapeziform, heart-shaped; beaks
distant, and separated by the angular groove of the ligament, which is
altogether external; hinge linear, straight, with small transverse
teeth, having at its extremity from two to five parallel ribs; valves
marked with minute and strong longitudinal striæ, and sometimes one
valve overlaps; margins crenulated.
_C. auriculifera._ The eared Cucullæa. Pl. 10, fig. 1.
Species navicular or obliquely heart-shaped, with decussated striæ;
hinge completely straight, with two parallel ribs at each end, the
terminal teeth longer and more oblique than the others; exterior
chestnut colour, interior white, tinged with violet.