63 
CRENATULA. — Lamarck . 
Gen. Char. A subequalvalved, bivalve, flat- 
ish, lamellose, rather irregular ; hinge 
lateral, linear, internally marginal, crenu- 
lated ; crenulse arranged in a series, cal- 
lous, spoonformed, receiving a disjointed 
Ligament. 
The recent species of this Genus are flat shells, and 
composed of Lamellae, of a distinctly fibrous structure, 
which do not project beyond the surface, but mark upon 
it numerous, sharp lines much resembling those upon 
Inoceramus ; the hinge contains the characters in which 
it differs, it consists of a number of spoonlike pro- 
cesses, some of which, near the beaks, are placed close 
together, while others are distant, they receive de- 
tached portions of the ligament, and are not supported 
upon a distinct callus that, after being bent, extends be- 
yond the beaks as in Inoceramus ; those processes that 
are united together near the beaks, have still a furrow 
between the edges of their upper hollow sides, to which 
no ligament is attached ; this sulcus does not exist in 
Inoceramus, where one continued credulated grove in 
each valve appears constructed to receive an undivided 
ligament ; in Crenatula there is no great disproportion 
of thickness between the shell, about the beaks and mar- 
gin. Perna is distinguished from both the above men- 
tioned Genera, by having a sinus for the passage of a 
byssus. 
For other particulars my Brother’s work upon Genera 
may be consulted ; the above are sufficient to discrimi- 
nate fossils by. 
