MOLLUSCA. 71 
it serve to unite natural families. Lamark, without due con- 
sideration, regarded it as next in importance to the muscular 
impressions. 
The éeeth of the hinge of bivalves, since the days of Lan- 
gius, have been studied with care, and the characters which 
they furnish have been employed, both in artificial and na- 
tural arrangements, in the construction of the primary divi- 
sions. It would have been of some advantage tothe science, 
had conchologists ascertained the use of the teeth in the 
economy of the animal, before forming any divisions from 
their presence, absence, or position. They do not appear 
to be the index of any peculiar organization, neither can 
they be employed to bring together naturally allied families. 
The use of the adductor muscle is to close the shell; the 
ligament opens it; andthe teeth of the hinge seem destined 
to modify and direct these movements. The characters 
furnished by these three parts of the shell appear to be near- 
ly of equal importance, and fit only to occupy a very subor- 
dinate place. Were the circumstances connected with the 
teeth of the hinge to become the foundation of the higher 
divisions, many natural families would be broken. Thus, 
the genus anodonta would be removed from the unio, al- 
though they are both fluviatile, possess one long subulated 
foot, one syphon in the form of a hole, the summit of the cloak 
furnished with cirri, the branchiz in part re-united, vivipa- 
rous, carrying the young in the branchiz. In short, it seems 
to be a character fit only for generic and specific distinc- 
tions. 
Bivalve shells have often been divided into equilateral 
and inequilateral. These differences do not appear to be 
the signs of any peculiar character of the animal, or any of 
its functions. They must influence, to a certain extent, the 
