18 UNIONID&. 
5. P. ROSEUM (rose-tinted). 
Somewhat oblong, tumid, 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.—UNI0ONID&. 
Genus I—Unto. 
1. U. rumipus (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. pictérum (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. 
