70 BIVALVES MYTILUS. 



inspection of the hinge, the error will soon be dis- 

 covered. 



Muscles differ greatly in external appearance, some 

 being perfectly smooth, and beautifully marbled and 

 variegated with delicate colors; others elegantly ra- 

 diated with purple and white; and a third class 

 being of one color only, as black, blue, green, yellow, 

 or brown, and coarsely ribbed and grained with mi- 

 nute tubercles. In the greater part the coloring is 

 confined to the epidermis ; when this is removed, and 

 the shell polished, so different a surface is presented, 

 that an adept would be puzzled to decide to what species 

 it should be referred. In some specimens the epidermis 

 is shaggy or bearded. 



Many exhibit internally a pearly appearance, and 

 some, when uncoated and polished, display considerable 

 brilliancy. The M. margaritiferus is celebrated for its 

 iridescent colors, and is, moreover, valued for the beau- 

 tiful and costly pearls it produces. The young shells 

 of this species are sometimes so different to the adults 

 in appearance, that they can scarcely be recognised as 

 being the same. 



The M. edulis is found in immense beds or layers, and 

 invariably afiixes itself to other bodies by means of its 

 silky byssus. 



The M. cygneus and M. anatinus, (both fresh-water 

 species), frequently become the prey of birds: when 

 the shell is too hard to be penetrated by their beaks, 

 they mount with it to a considerable height, and by let- 

 ting it fall, are enabled to pick out the fish from the 

 broken shell. 



