MOLLUSC A. 71 



it serve to unite natural families. Lamark, without due con- 

 sideration, regarded it as next in importance to the muscular 

 impressions. 



The teeth 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 to the 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;and s the 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 branchiae in part re-united, vivipa- 

 rous, carrying the young in the branchiae. 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 



