BIVALVES. MYTILUS. 63 



is removed, so different a surface is often presented, that 

 even an adept might be puzzled to recognize tvv^o shells 

 of the same species. In some specimens the epidermis is 

 bearded or shaggy. In a few instances, the valves gape, 

 as in the M. bilocularis, and other similar species. 



The greater part of this genus exhibit internally a 

 pearly appearance, and some (when uncoated and pohsh- 

 ed) afford the brightest radiance possible. The M.mar- 

 garitiferus is admired for the iridescent colors it displays, 

 and is, moreover, famous for the fine and valuable pearls 

 it engenders within its silvery valves. The young shells 

 of this species, are sometimes so different to the adults in 

 appearance that they can scarcely be known for the same. 

 Some of the Mytili possess the faculty of penetrating 

 coral-rocks, hard marble, and limestone. Of this class 

 are the M. lithophagus and M. rugosus; the latter is 

 sometimes found in lakes as well as the sea. 



A few species, on a superficial glance, might be mistaken 

 as belonging to the genus Mya; viz. the M. versicolor, M. 

 discors, and M. afer; but, by a minute inspection of the 

 hinge, the error would soon be discovered. 



The M. edulis affixes itself to other bodies, by means of 

 a silky byssus; it is found in immense beds or layers, con- 

 sisting of many myriads. 



The M. crista-galli, &c. form exceptions to the general 

 habits of the shells of this genus, for they attach them- 

 selves to Gorgonia and other bodies by a formation of 

 the shell itself, which has the appearance of several dis- 

 tinct claws or hands. The M. cygneus and M. anatinus, 

 (both fresh-water species), frequently become the food of 

 birds and aquatic fowls. 



The Mytili from the rivers in Africa, are often of great 

 beauty when polished, and exhibit fine colors. 



