GINGLYMACONCHA. PECTINIDZ. 341 
FAMILY II. PECTINID. 
Shells most often nearly equivalve; the hinge toothless ; 
the ligament internal, situated in an exeavation more or less 
triangular ; the upper margins of both valves alated (winged) 
before and behind ; the epidermis very thin. 
The mantle is separate, not at all jomed; its margin frmged 
with a double row of cirri, ornamented with round emerald- 
coloured spots, resembling eyes; no trachea; the lips furnished 
with tentacles, but not lobated ; the foot is oval, truncated, 
and bearing a byssus at its extremity. 
All the Pectinidzee inhabit the sea; their shells are most 
generally slightly mequivalve, which arises from the superior 
convexity of one of the valves, or from the notch in the right 
valve, for the exit of the byssus. The hinge has no teeth; the 
ligament is internal, being placed on an excavation more or 
less triangular: their upper margin has an auricular dilatation 
before and behind the umbones, which are nearly central. 
Genus 69. PECTEN. 
Shells regular, inequivalve; the superior margin straight, 
dilated before and behind into a wing-like process; the umbones 
contiguous and central; the hinge toothless; the cardinal ex- 
cavation (or fovea) trigonal, situated far inwardly; receives the 
cardinal ligament, which is concealed ; the right valve at the 
exit of the byssus notched. 
This genus contains a vast number of species, and is divided 
into several sections or subdivisions, of which I shall only enu- 
merate those peculiar to the British ones, that the characters 
of the sections may not be confounded or mistaken for those 
belonging to those of the species. 
In the first two sections may be observed, at the base of the 
auricular processes, before and behind in each valve, an obtuse 
tubercular process, which cannot be observed in any of the 
other sections. 
