How to obtain it. 



217- 



rivers unless they are deep and slow flowing. It has a long pointed 

 spire to the shell, and is one of the largest of the genus, attaining 

 under favourable conditions, a length of one-and-three-quarter 

 inches. There are a number of others of this class that are 

 both beautiful and interesting to collectors, but for practical 

 importance the first mentioned (L. pereger) is decidedly the most 



A 



flf 



iiffiis stagnalis. 



^ ' 35- Planorbis come us. 



useful. The round flat shell fish (Pianorbis) are useful and in 

 some waters abundant, but they do not grow so fast nor breed 

 so plentifully as the Limnea. There is a useful little limpet, that 

 when once established multiplies rapidly in shallow cold water, 

 where the other snails do not thrive so well. This is Aucylus 

 fluviatilis. Fish have often been taken in brooks with these 

 molluscs in their stomachs. 



Fig. 36. Ancyliis 

 Jluviati is. 



Fig- 37- Palndinn vh>ifera. 



The Paludina are larger snails, but are ovoviviparous ; that 

 is, they keep their eggs within their shells until they are hatched. 

 They are also possessed of a hard horny plate to close the entrance 

 of the shell, called an opercuhim, and the shell itself is thick and 

 strong, and fish will probably not eat them, at least when mature. 



