spire-shells and Marsh-snails 235 



considered in this chapter causes us to jump fre- 

 quently from the seashore to the estuary and the 

 inland waters. So, also, from considering some of 

 the smallest of our native species we have now to 

 mention the largest of the fresh-water gill-bearing 



River Snails, Fivijyara; male on left, female on right, young (magnified) in front 



mollusks — the River Snails {Vivipava). Like many 

 others that have been under notice the animal has a 

 prominent snout, the eyes are placed outside the base 

 of the tentacles (in this case on short stalks), the 

 shell has a symmetrical spire, and an oval mouth, 

 closed by a horny concentric operculum. They are 



