102 POPULAR CONCHOLOGY. 



valve/ inequilateral ; hinge straight, with either 

 no teeth or mere rudiments ; shell transverse ; 



ligament external. Animal resembling that of 

 the Unio. — 15 species recent. 



They lie buried in the sand or mud of lakes 

 and ponds, and are found distributed in every 

 quarter of the world ; the valves are thin and 

 large, pearly, and covered with an epidermis. 

 From their shape and lightness they are used 

 in France for skimming milk. 



62. Iridina. — Shell equivalve, inequilateral; 

 hinge very long ; teeth 

 small, like little tuber- 

 cles, and numerous; very 

 iridescent; ligament ex- 

 ternal. Animal, foot 

 compressed and sharp, — 1 species recent. 



