GASTROPODA. 



31 



pliorescent. Like the Snails, they are fond of damp localities, and 

 at times become great pests to farmers in devouring the young 

 shoots of the growing corn. Testacella, which is found in this 

 eountry, differs from the Slugs in having an external shell at the 

 tail-end of the foot. It is not slimy, and lives under ground, 

 feeding upon earthworms. 



The first group of the aquatic air-breathers, the Auriculida, [Case 

 -chiefly inhabit salt or brackish water. The largest forms are 17 a.] 

 tropical and found at the mouths of rivers, among the roots and 

 stems of mangrove-trees, or in damp woods near the sea. 



The Limnmda? are only found in fresh water. Most of them [Case 

 occasionally rise to the surface to breathe, where they glide along 17,b-d.] 

 foot uppermost, at times suspending themselves by a glutinous 



thread, after the fashion of a spicier, 

 their peculiar species. 



Fiff. 20. 



All countries appear to have 



British Pond-Snail (Limntsa staff nalis). 



1. Upper view : a, foot ; b, tentacles ; c, eye ; d, muzzle. 



2. Lower view : letters a, b, c as above ; e, mouth ; /, respiratory orifice. 



The freshwater Limpets (Ancylus) live attached to stones and [Case 

 leaves of plants, and have not the habit of floating, but, like the 17 d.] 



