MOLLUSCA OR UNIVALVES. 181 



# 48. Cyclostoma. — Shell either flattened 

 or turreted ; mouth cir- 

 cular; the margin of 

 both lips united, and 

 slightly turned back ; 

 closed by a shelly or 

 horny operculum. Ani- 

 mal, head having two tentacula with eyes at the 

 base ; foot oblong. — 45 species recent, and 10 

 fossil. 



These shells vary much in form, some 

 being very flat, others having the apex length- 

 ened out, and being more conical ; they all have 

 the mouth round. 



The Cyclostomata are found principally in the 

 torrid zone ; but one species, the Cyclostoma 

 elegans, is a native of Britain : they inhabit 

 woods, and are found amongst moss, stones, 

 &c. 



Family 2. — Lymnmda* 



This family consists of amphibious animals 

 with two tentacula, having eyes at the base. 

 They inhabit fresh water, and rise to breathe 



* Les Lymneens, Lamarck. 

 K 3 



