198 LAKES AND RIVERS. 



less glossy, and it is striated irregularly, but finely, de- 

 noting the stages of growth, the colour is cinereous or 

 yellowish-white, the length is 0*175, breadth 0*2; 

 it inhabits mossy swamps, ditches, and drains, and 

 is generally diffused; the variety obtusalis is less 

 frequent. 



The body of nitidum is " whitish, with sometimes 

 a tinge of yellow, caused by the colour of the liver," 

 the foot long, the mantle bordered with gray. The 

 shell is thin and iridescent, striated concentrically; 

 the colour yellowish-white, or light horn ; the epi- 

 dermis "a mere film;' 7 the hinge, as in the two last- 

 named species, is short and strong ; its habitat is also 

 similar. There is a fine variety, nearly half as large 

 again, of a lemon colour. 



P. roseum has the body of opaline colours, the foot 

 long and semi-transparent ; the shell is glossy, yel- 

 lowish-white, and the epidermis is very thin ; the 

 inside of the shell is nacreous-white, the hinge-line is 

 nearly straight, the cardinal teeth are very small, the 

 lateral teeth are sharp at the edges, otherwise not 

 well developed ; the scars, when the animal is re- 

 moved, are scarcely visible ; the length is 0*1, the 

 breadth is 0*15. It inhabits localities similar to the 

 preceding species. 



The Unionida are often called fresh-water mussels. 

 Some species are ovoviviparous, others oviparous, 

 like most molluscs, and are believed to be monoe- 

 cious. They live in rivers and large pieces of 

 water, and with their large fleshy foot they move to 

 considerable distances. In summer, when the 

 streams are shallow, they bury themselves in the 



