82 POPULAE BRITISH CONCHOLOGY. 



The Cycladid^ are ^m-iii}^ fresh-water molluscs, with more 

 or less oval shells of a horny structure, having cardinal and 

 lateral teeth in each valve. By the sides of rivers, in ponds 

 and ditches, buried in the mud, live these little bivalve 

 shell-fish, bringing forth their young from eggs within the 

 parent shell. 



I. Cyclas has a long foot and divided siphon. The shell 



of 

 C. vivicola is oval, inflated, and striated; that of 

 C. cornea is more rounded and smooth ; while that of 

 C, caliculata has a peculiar cup-shaped prominence on the 



umbo. 



II. PisiDiUM has the siphonal tube single. While in Cyclas 



the hinge of the shell is placed on the longer side, 

 that of Pisidium is on the shorter. The British species 

 are — P. ohtusale, P. pusillum, P. cinereimi, P. nitidum, 

 P. j3ulchellu7n, P. Henslowianum, P. amnictim, with 

 differences too minute to be otherwise than technical. 



