116 



PECTEN. 



OSTREA MAXIMA. LitM. 



Mawe's Linneeus y plate 14, Jig. 1, 2, 4, 6. 

 In this genus the apices are approximated and nearly 

 contiguous, without any angular separation between 

 them, and the cavity for the ligament is altogether inter- 

 nal. The shells of this family are extremely numerous, 

 very beautiful, and so well known to every collector, 

 that a minute description of them is not here requisite. 

 The valves are regular, in general flattened, but often 

 not equivalve, one being frequently more convex than 

 the other, with longitudinal radiating ribs from the 

 apex to the margin ; flat, smooth, or armed with vaulted 

 spines, imbrications, or striae, of every possible form ; the 

 marginal edges entire, smooth, or crenulated, generally 

 interlocking in each valve: they are auriculated, and 

 the posterior side with the largest ear, beneath which 

 the sinus is placed: substance solid and thin. Lamarck 

 does not mention that in some species the flat upper 

 valve drops into the lower to a considerable depth; nor 

 the very dissimilar form of the P. Pleuronectes and its 

 congeners, in which the valves never close, and, though 

 ribbed within, are smooth on the exterior surface. 



