142 POPULAR BRITISH CONCHOLOGY. 



shell is round and horny^ much shorter than PalucUna or 

 BitJiinia. The animal deposits her eggs in a little leather 

 bag, which she hangs on stones or the stems of water-plants, 

 where they remain till they are hatched and liberated from 

 their bag by the bursting of its rotting sides. They all leave 

 their prison in company, being united in a floating mass of 



jelly- 



The shell of Valvata cristata, our only other species, has 

 a flattened spire. 



