BIVALVES. PINNA. 65 



Undatus — Waved. Stagnalis — Fresh-water. 



Purpureas — Purple. Zellensis — Geenuh-yellow. 



Saxatilis — Rock. Roseus — Rosy. 



Argenteus — Silvery. Puniceus — Ventricose. 



Fulgidus — Shining. Niger — Black. 



Azureus — Azure. Laevigatus — Smooth. 



Murinus — Mouse-colored. Dubius — Doubtful. 



Testaceus — Testaceous. Polymorphus — Cellular. 



Virgatus — Striped. Canaliculatus — Canaliculated. 



Cordatus — Heart-shaped. Rostrum — Sharp-beaked, 

 Camelli — Camelli's. 



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



Animal — aLimax; Shell bivalve, fragile, upright, ff aping 

 at one end, and furnished with a hyssus or heard ; 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 ahke, as barely to 

 admit of being called distinct. 



The usual form of the Pinnae is allied to that of the 

 larger species of muscles, being long and tapering, narrow 

 at the beaks, and gradually expanding to a considerable 

 breadth at the opposite extremity: there are some in- 

 stances where the form is more compressed. 



The Pinnse are by no means so entire or solid as the 

 muscles, for they are (with few exceptions) exceedingly 

 brittle or fragile in substance, and almost invariably gape 

 at one end. 



