BIVALVES. MYTILUS. 71 



might be puzzled to recognise two shells of the same spe- 

 cies. 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 polished) afford 

 the brightest radiance possible. The M. margaritiferus is 

 admired for the iridescent colours it displays, and is, more- 

 over, 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 in the sea. 



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

 as belonging to the genus Mya; viz. the M. latus, M. dis- 

 cors, and M. ungulatus ; 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. 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 colours. 



The Indian, Atlantic, American, and Northern oceans 

 produce many species; some are also from New Zealand, 

 the Mediterranean, Russian, and Red seas. 



