SNAILS AND MUSSELS 



Fig. 253. — Fresh water limpet, Ancylus parallelus 

 (Ferrissia parallela of Baker): i, shell from above 

 showing the parallel sides; 2, the low cone in side 



view. 



oJpt-i- 



Fig. 254. — Fresh water limpet, Ancylus rivularis 

 {Ferrissia rivularia of Baker): i, shell from above 

 showing the slight flare of the front end ; 2, side view- 

 Fresh water limpets, Family Ancylidae. — The shells are 

 small, about one-fifth of an inch long, shaped like a low cone. 

 The animal has short blunt tentacles and a very large oval 

 foot. It has a lung-sac like other air-breathing snails but 

 also has a cone-shaped gill or pseudobranch extending out 

 beyond the shell on the left side (Fig. 252). These snails live 



Fig. 255. — I, Shell of Amnicola limosa; 2, animal 

 of Amnicola limosa porata, showing the truncated 

 foot and slender tentacles; 3, operculum of the 

 last variety, greatly enlarged (2, 3 after Baker). 



313 



