46 PALAEONTOLOGY OF CALIFORNIA. 



FAMILY PECTINIM. 



Genus PECTEN, Mtiller, 1776. 

 Pecten acutiplicatus, Meek. 



PI. 8, Fig. 3. 



The only specimen of this species in the collection consists of an impression 

 of apparently a left valve, in the hard matrix. Owing to the fact that the ears 

 are imperfect, it is very difficult to determine, beyond doubt, whether it is a left 

 or a right valve, though the slight obliquity of the plications, and the appearance 

 of the remaining portions of the ears, indicate that it is the former ; while its 

 very slight convexity goes rather against this conclusion. It may be charac- 

 terized as follows : 



Subovate, compressed^ longer from the hinge to the ventral 

 margin than the antero-posterior diameter; sides converging 

 from near the middle to the beaks, at an angle of about 80° ; 

 ventral and ventro-lateral margins regularly rounded ; ears flat- 

 tened, anterior? one with two or three small radiating costae, 

 and the posterior with one rib near the hinge margin; both 

 marked with fine striae of growth. Body of the valve orna- 

 mented by fourteen to fifteen regular, simple, sharply elevated, 

 angular^ radiating plications, equalling in size the angular fur- 

 rows between; crossing the whole are numerous very fine, 

 crowded striae of growth, which are deflected so as to follow a 

 zigzag direction, as they pass over the plications and across the 

 depressions between* 



Diameter from the hinge to the ventral margin, 2.50 inches; 

 antero-posterior diameter} 2.15 inches; convexity (left valve?), 

 0.35 inch. 



This species belongs beyond doubt to the genus Pecten, as usually understood by 

 most authors ; but does not, however, belong to that genus, as properly restricted 

 by Lamarck, in 1799, to such types as P. jacobceus, which must be regarded as the 

 type of the genus. Having no means of knowing to which one of Prof. Agassiz's 

 unpublished genera of Pecienidce it belongs, it is placed here for the present in the 

 genus Pecten. 



