MELANIA. 165 



of that dark clingy colour which more or less characterizes 

 the shells of all water mollusks ; they are, also, generally 

 eroded. 



Several varieties have been discovered in the great rivers 

 of America. 



Why is it that throughout the domains of nature, with 

 the exception, we believe, of fishes, some instance of perfect 

 black occurs in each ? Mollusca are not exempt ; the shell 

 of the genus Melanops'is is covered with a deep black 

 epidermis, and presents in this respect a singular contrast 

 to the exquisitely tinted coatings of some other species. 



In Melauojms the shell is fusiform, or conically cylindrical, 

 covered with a black epidermis ; the apex is sharp, the 

 columella smooth, often thickened towards the upper part, 

 and more or less truncated at the lower ; aperture generally 

 oblong, acute and somewhat canaliculated above and deeply 

 sinuated below, lip a little reflected, and the operculum 

 horny, spiral, and small. 



Such, by river-side or stream, in deep sea-caves, and 

 along the shores of this and other countries, are different 

 members of the Order Pectinihranchlata. 



