This genus possesses the same faculty of boring rocks as the Saxicava;
it is distinguished from the latter genus by the hinge having one or two
teeth in each valve.
Shell sub-trigonal, transverse, inequilateral; upper side narrowed and a
little gaping; lower side rounded.
Petricola lamellosa.
P. ochroleuca.
P. semilamellata.
P. lucinalis
P. striata.
P. costellata.
P. rocelaria.
P. exilis.
P. ruperella.
P. chamoides.
P. pholadiformis.
P. labagella.
P. linguatula.
_P. lamellosa._ The lamellous Petricola. Pl. 7, fig. 3.
Species oval, trigonal, radiated; two teeth on one valve, and one on the
other.
_P. pholadiformis._ The Pholas-shaped Petricola.
Species transversely elongated.