138 POPULAU BRITISH CONCHOLOGY. 



black ; the foot is broad in front and rather tapering at the 

 back; the operculum is half-moon-shaped, shelly, with a 

 little spire and a key-like process, which fits under the 

 straight columella of the shell. This is the shell which is 

 often picked up by the children from sand-heaps in a half- 

 fossil condition. 



PALUDINIDJE. 



I. Paludina. — In dried specimens of I^aludma frequently 

 met with in cabinets, we sometimes find several glassy, round 

 shells, adhering by the dried mucus to the inner surface. 

 This results from the habit of the female, which gives one 

 of the species its name of vivipara. The eggs are not only 

 kept in safety until they are hatched, but the young fry is 

 also preserved within the shell for some time after they leave 

 the ^^^, and their testaceous transparent bubble is fully 

 formed. When very minute, they are covered with bands of 

 hairs, which disappear in the course of a couple of months, 

 when they are sent adrift to seek the means of future exist- 

 ence for themselves. It has been ascertained that, during 

 the reproductive season, which commences in autumn, only 

 two, three, or four young Paludinm are sent forth from the 

 parental roof in the course of twenty-four hours ; so that 



