This genus resembles the Ostrea, with which it was formerly classed, but
from which it is distinguished by the peculiar character of the lower
valve. It is very deep and carinated, with a summit terminating in a
long spirally recurved beak, slightly turned to one side; the edge sharp
and angular.
It is seldom, if ever, attached to other bodies. Shell more finely
lamellated than that of the oyster, free or slightly adherent,
sub-equilateral, very inequivalve; the lower valve very concave, with a
summit more or less recurved like a hook; the upper valve much smaller,
and formed like a lid; hinge without teeth; ligament inserted in an
oblong arched cavity; one single muscular impression on each valve.
_G. angulata._ The angulated Gryphæa. Pl. 16, fig. 2.
Oblong ovate, with three long longitudinal carinated ribs below; summit
of the inferior valve is subvolute. This is a rare shell.