196 LAKES AND RIVERS. 



narrow, the inside is ashy-white, the teeth resemble 

 those of corneum, but are very small. The scars 

 left by the adhesion of the animal to the shell are 

 faint. Its habitat is the Exemouth, the Paddington 

 Canal, and the ponds and canals of Lancashire. 

 "A living specimen taken in February, and kept in a 

 vessel by itself, gave birth to several young, which 

 were immediately very active, and used their long foot 

 like a leech. They seemed to be fond of nestling 

 under their mother for the sake of shelter or shade." 

 The shells are slightly iridescent. 



S. lacustre, the fourth species, is 0-3 long, and 0-4 

 broad ; the body is whitish, tinged with rose colour. 

 The foot is nearly twice as long as the shell, which is 

 nearly round ; the mantle is fringed with gray, the 

 epidermis is very thin, the shell is very thin, horn or 

 grayish colour, with sometimes darker zones, and is 

 iridescent. The anterior and posterior sides are cut 

 off and slope towards the front margin. The inside 

 is bluish-white. They generally inhabit lakes, ponds, 

 and stagnant water in England, Wales, and Ireland. 

 These animals are interesting in their habits in cap- 

 tivity ; they possess the power of spinning transparent 

 threads, by which they attach themselves to water 

 plants, and have other interesting manners which space 

 will not permit us to describe. 



The genus Pisidium, the name signifying pea- 

 shaped, was established to divide from Sphcerium^ 

 the smaller species, which have only one tube or 

 siphon, and whose shells are less equilateral. The 

 general shape of the shells and size of the beaks 

 are said by Jeffreys to be the only reliable method of 



