206 CO^CHYLlA—niTHYRA. 46.. 



it is frequently deformed and distorted by contact and harder 

 objects. It may perhaps be a distinct species ; as it answers to 

 the character ^iven by Lamarck, Hist. Nat. vi. p. 209, to his 

 Ostrea deformis. 



46. PECTEN— LISTER. 



Testa libera seujixa, suhorhicularis , bast transversim auricu- 



latd ; nmbonibtis contiguis a;qualibus. Car do edentulus, fovea 



interna trigond. Ligatnentum internum. 

 Shell free or fixed, somewhat orbicular, transversely dilated into 



auricles at the base ; with the beaks equal and close tou;ether. 



Hinge without teeth, with an internal triangular cavity. Li- 



jrament internal. 



The ear-like appendages at the sides of the beaks distinguish 

 this family from that of the Ostrea. These auricles have gene- 

 rally one of the edges fringed with small sharp spines ; whereas 

 the Ostrea is furnished with minute internal crenatures on each 

 side the hinge. They are mostly ribbed longitudinally, and with 

 the exception of Pecten sinuosus and P. Pusis, are free, and 

 capable of considerable locomotion ; and they exhibit a more 

 splendid and varied display of colors than any of our native genera. 



