18 UNIONIDJE. 



5. P. ROSEUM (rose-tinted). 



Somewhat oblong, tnmid, glossy, regularly striate con- 

 centrically ; ligament almost invisible. 



Its habitats are similar to those of the last species. 

 Its oblong shape, the situation of the beaks, which are 

 on one side like those of P. fontinale, and the straight- 

 ness of its lower margin, serve to mark it off from P. 

 nitidum, which it somewhat resembles. 



Family II. UNIONID.E. 

 Genus I. UNIO. 



1. U. TTTMIDUS {swollen). 

 Ovate, very solid, dark brown ; epidermis smooth. 



Found in rivers, ponds, and canals in England and 

 Wales commonly. 



Var. I. radiata. Thinner, radiated with yellow. 

 Var. II. ovalis. Wedge-shaped, dark coloured. 



2. U. PICTORUM (Painters'). 



Oblong, solid, usually narrower than U. tumidus. The 

 ligament is parallel with the lower margin, whereas the 

 ligament of the last species, if produced, would meet the 

 line of the lower margin, and form an angle. (See plate.) 

 Its colour is usually a much brighter green, and it is more 

 glossy than the last species. It is also narrower in pro- 

 portion to its size, and less solid. 



