76 CONCHOLOGY. 



truncated ; valves rather rounded at the upper end, and in 

 the shape of an expanded fan ; hght fawn colour. 



P. pectinota. The pectinated Pinna. PL 13, fig. 1. 

 Thin, pellucid ; longitudinally ribbed and spinous for half 

 its width, obliquely striated transversely on the other half. 



FAMILY X V 1 1. 



Malleacea. Five genera. 



1. Crenatula. Seven species. 



There is one peculiar distinction between this genus and 

 the Perna ; the hinge of the Crenatula is composed of 

 slightly concave callous crenulations, which receive the hga- 

 ment ; while in the Perna it consists of parallel truncated 

 linear teeth (or, rather, riblike joints), corresponding and op- 

 posed to the opposite ones, the ligament being inserted only 

 in their interstices. 



Shell thin, very delicate, irregular, valves flattened, folia- 

 ceous, sub-rhomboidal, sub-equivalve ; hinge longitudinal, 

 dorsal, witiiout teeth ; ligament sub-multiple, and inserted in 

 a series of rounded cavities corresponding with the dorsal 

 margin ; one sub-central muscular impression. 



Crenatula avicularis. Crenatula bicostalis. 



C. modiolaris. C. viridis. 



C. nigrina. C. mytiloides. 



C. phasianoptera. 



C. avicularis. The avicular Crenatula. PI. 14, fig. 2. 

 Answers to the above description. 



C. mytiloides. The muscle-shaped Crenatula. 

 Oblong, ovate, oblique; base acute ; violet coloured, with 

 obscure radiations. 



2. Perna. Ten species. 



In speaking of the Crenatula, we gave the characteristic 

 distinction, which regarded it natural and expedient to make 

 the Perna form a different genus. 



