so OS THE A. 



mals may not be specifically alike ; but the Linnaean 

 arrangement is professedly founded on the shells ; 

 and therefore^ when the hinge is much of the 

 same description, and the other characters are 

 not absolutely incongruous, it is surely unnecessary 

 to divide them otherwise than into sections, ac- 

 cording to their natural conformation. Neither, 

 in fact, are all the varieties of the species in each 

 division extremely dissimilar; for it is not at all un- 

 common to meet with specimens of the common 

 Oyster, Ostrea edidis, of a pectinated and eared 

 form ; so that a regular transition might be shown 

 from one to the other family. The third division 

 C is connected to the former ones by the O. Pes 

 Lutrce, which partakes largely of the properties of 

 both ; and differs from the 3d subdivision of A only 

 in the shape and direction of the groove which 

 constitutes the hinge, and in the thickness of the 

 valves which renders it not unlike the division B. 

 Strong locomotive powers have been attributed to 

 the Pecten, which are, it is said, exerted in a most 

 singular manner. A very rapid progress is effected 

 by the sudden opening and closing of the shell. 



