6'6 OSTREA. 



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, 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 

 uncommon to meet with specimens of the common 

 Oyster, Ostrea edidis, of a pectinated and eared 

 form ; so that a regular transition might be shewn 

 from one to the other family. The third division 

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

 Lutra, 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. This is done with so much muscular force. 



