150 BIVALVES. 



a bifurcated* tooth in the other valve ; shell 

 about two inches long, and four broad ; covered 

 with a black epidermis decorticated^ at the um- 

 bones ; inside of a greenish pearly hue. 



This shell is one of a very interesting group, 

 now formed into a distinct genus and called 

 Unio. It inhabits only rocky torrents, and the 

 precipitous streams of mountainous districts. 

 Many are found in the cataracts and rapid rivers 

 of America, and by their solid and thick shells 

 manifest the providential care that fitted them 

 for the dangerous spots they occupy. When we 

 look at the ponderous Mya driven by the power- 

 ful torrent, and compare it with the light and de- 

 licate lanthina, borne gently on the surface of the 

 waves, shall we coldly attribute such adaptation 

 to circumstances or the blind dealing of chance, 

 and not rather delight to recognise the benefi- 

 cent wisdom of our heavenly Father, pervading 

 all his works, and suiting each to the place he 

 assigns it 1 



The Mya Margaratifera is found in several of 

 our rivers, particularly those of Wales ; also in 

 Ireland, where the peasantry use the valves as 

 spoons. This species has long been celebrated 

 for producing pearls of a good colour, and some- 

 times of a considerable size. These ornaments 

 appear to be exclusively the production of the 

 Bivalve testacea, and are found only in the shells 



* Bifurcated, having a fork of two teeth : from the Latin bis, 

 twice ; and furca, a fork. 



t Decorticated, having the bark or outer skin taken off j from the 

 Latin de, off : and cortex, the bark of a tree. 



