ORDER TESTACEA. 99 
other in the two valves, and lodging as many elastic liga- 
ments; the irregular and foliaceous shell marked on the 
anterior side beneath the hinge by a notch traversed by 
the byssus. The perne were also left by Linnzus among the 
ostrez. 
CRENATULA, Lam. 
The crenatula, lately separated from the perne, instead of 
having transverse cavities on a broad hinge, are furnished 
with oval ones on the very margin, where they occupy but 
little of its breadth. The byssus seems to be wanting; and 
they are frequently found among sponges. 
It is thought that we may approximate to the perne, cer- 
tain fossil shells, in which the hinge is also furnished with 
cavities, more or less numerous, that correspond to each 
other, and thus appear to have furnished points of attachment 
to ligaments; thus, those of the 
GERVILLIA, Defr., 
Have a shell closely resembling that of the vulselle, but with 
a kind of double hinge, externally with opposed cavities, re- 
celving as many ligaments, and internally furnished with 
very oblique teeth in each valve. Their impressions are 
found along with ammonites in compact limestone. 
INOCERAMUS, Sowerb., 
Ts remarkable for the elevation and inequality of the valves, 
the summit of which curves in a hook towards the hinge; 
their texture is lamellated. 
CaTILLuS, Brong., 
Independently of the depressions for the ligament, the 
eatilli have a conical furrow sunk in a rim, which is bent at 
a right angle, to form one of the margins of the shell. ‘The 
H 2 
