Our British Snails 49 



is horseshoe-shaped. The lip is thin and not 

 reflected. 



The genus Vertigo (i.e. twisted, the Latin equiva- 

 lent of the Greek Helix) contains shells even smaller 

 than the Pupae, about the size of a pin's head. 



Vertigo [AIcbo) antivertigo [i.e. not reversed 

 or sinistral, as are V. pusilla and V. angustior). 

 Semi-transparent, glossy, horn-colour, with den- 

 ticles (as have all except V. edentula and V. 

 minutissima) . Found in nearly all counties in 

 moist places. 



Vertigo [Alee a) nioulinsiana. — Our largest 

 species, though only 2 J miflimetres in height. 

 Mainl}^ in marshy places. Not common. 



Vertigo [Alcea) alpestris. — Rare and local, 

 chiefly northern. Nearly transparent shell. 



Vertigo [Alcea) pygntcea. — Common, and often 

 in colonies at roots of grass and under stones and 

 logs. Not confined to moist places. 



Vertigo [Alcea) suhstriata. — Local. Strongly 

 striated. 



Vertigo [Vertilla) pusilla. — Sinistral, as is also 



Vertigo [Vertilla) angustior. — Both species rare 

 and local. The former is the larger and broader. 

 In the former the last whorl is broadest, in the 

 latter the penultimate. In the former the mouth 

 is semi-oval, in the latter triangular. In the 

 former the outer lip is very slightly, in the latter 

 very deeply contracted. The former has 6 to 7 

 teeth, the latter 4 to 5. 



D 



