88 POPULAE BRITISH CONCHOLOGY. 



curious chase. The mantle of the animal is plain, and freely 

 open ; the lips of the anal siphon form a tube-like projection ; 

 and the branchial opening is fringed by filaments : the shells 

 are pearly within, and covered by a thick, horny, smooth, 

 brown or green epidermis without. 



I. Unio has a thick oval shell, with teeth on the hinge : 



the soft parts of many of the magnificent species of 

 foreign rivers are used for food. 



U. tumidus has an oval, obliquely angular shell, with wavy 

 tubercles at the umboes. 



Z7. joictorum is much longer, and less oblique. 



U, margaritifera, or Pearl-bearing Unio, has the shell long, 

 arched, with a black epidermis. In the Conway, the 

 Pirth, the Tay, and other rivers, are found the haunts 

 of these animals, where they are sought for their pearly 

 products, occasionally, at rare intervals, rewarding the 

 seeker with a prize worth a pound or two. 



II. Anodonta is represented by one species among our 



Islands, the A. cygnea : the shell is light and thin, of 

 a varying, but generally oblique oval shape ; the hinge 

 without teeth, and the outer surface covered with a 

 glossy transparent epidermis, brightly rayed with green. 

 The Mytilid^ are true mussels, generally inhabiting the 



