5 8 Our British Snails 



water. A parasite of this mollusc causes " fluke " 

 in sheep which have taken it in by drinking or 

 by eating grass by the side of ponds and ditches. 



Limncea {Omphiscola) glabra. — Also amphibious. 

 About the same size as tnincatula. Local. 

 Inner lip rather thick and reflected on the base 

 of the penultimate whorl. 



Limncea {Ancylus) fluviatilis, — " Freshwater 

 limpet." Shell, rather limpet-like, with a hooked 

 apex (whence its generic name) , adheres to stones 

 or piles in running water. Common. I once 

 dredged a large water-beetle with three of these 

 shells adhering to its wing-cases ; thus it would 

 be transported to fresh habitats. 



LimncBa {Acroloxus) lacustris. — Like the former 

 but more local, and preferring sluggish or still 

 waters. Shell more oblong, thinner, and apex 

 twisted to the left instead of to the right as in 

 fluviatilis. 



The sub-order Pectinibranchiata (comb-like 

 gill) contains the genera Neritina, Paludina, and 

 Valvata, in all of which there are two tentacles 

 with eye at the base, and an operculum to the 

 shell. 



Neritina fluviatilis. — Solid, glossy, chequered 

 brown, white, and purple (but also a lemon- 

 coloured variety). Operculum semi-lunar, orange, 

 with a projection which serves as a lock to keep 

 the operculum in position. Not rare in England ; 

 on stones in running water. See illustration 



