The common name was given to this genus from the resemblance to a French
shepherd’s crook. The shell is of a regular form; its lower valve, in
which is a sinus for the byssus, is turned up at the edges, and the
upper valve falls within it.
Shell inequivalve, a little eared; apices unequal, distant, rounded,
little evident; hinge without teeth; ligament inserted in an oblique
groove, prolonged to the summit, and carried within in a kind of
spoonlike cavity.
_P. spondyloideum._ The spondylus-shaped Pedum. Pl. 15, fig. 5.
Ovate, wedge shaped, flat; superior valve with longitudinal striæ;
white, granulated, and rough; slightly tinged with purple near the beak.