MOLLUSC A OR UNIVALVES. 185 



52. Ancylus. — Shell oblong, small and 

 transparent; apex rather pointed, 

 and bent to the right, somewhat Jl 40* 

 resembling a Patella in form ; but 

 the apex is posterior, whereas that of the Pa- 

 tella is anterior. Animal, head very large, 

 having two tentacula, with eyes at the base ; 

 foot large. — 5 species, recent and fossil. 



The Ancylus is found only in fresh water, 

 in ponds and brooks, where it attaches itself to 

 flags and other aquatic plants, and also to 

 stones. It swims about on the surface of the 

 water, with the back downwards. It is nearly 

 amphibious ; for in summer, when the brooks 

 are dried up, it remains in the soft mud until 

 the return of rain. It is also often found out of 

 the water, and only within reach of the spray 

 of a waterfall.* 



* Turton's Manual. In Lamarck's system this shell is 

 placed with the Calyptraciens ; but it is now ascertained 

 that the animal greatly resembles the Physa in form and 

 habits, and it has therefore been removed to the family 

 now described. 



