66 O ST RE A. 



mals may not be specifically alike ; but the Linnnean 

 arrangement is professedly founded on the shells; 

 and therefore, when the hinge is much of the 

 same descrij)tion, and the other characters are not 

 absolutely incongruous, it is surely uimecessary to 

 divide them otherwise than into sections, accord- 

 ing 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- 

 comnion to meet with specimens of the common 

 Oyster, Ostrea edulis, of a pectinated and cared 

 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. PcsLutrce, 

 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 thicknessof the valves which 

 renders it not unlike the division B. 



Strong locomotive powers have been attributed 

 to the Pectcn, which are, it is said, exerted in a 

 most singular maimer. A very rapid progress is 

 effected by the sudden opening and closing of the 

 shell. This is done with so much muscular force. 



