BIVALVES. PINNA. 



C5 



Caniellii. 



PINNA. — Fin Shell or Nacre, also Sea- Wing. 



A nimal'-a Limax ; Shell hivalveyfragiUy -upright, gaping 

 at one ejid, and furnished with a h/ssusor beard; hinge 

 without teeth, the valves united into one. 



The number of species contained in this genus is limited 

 to eighteen, and some of those are so alike, as barely to 

 admit of being called distinct. 



The usual form of the Pinnas is something allied to that 

 of the largerspecies of muscles, being long tapering shells, 

 narrow at the beaks, and gradually expanding to a con- 

 siderable breadth to the opposite extremity: however, 

 there are instances where the form is more compressed. 



The Pinnae are by no means such entire or solid shells 

 as the muscles, for they are (with few exceptions) exceed- 



