44 The Shell-Collector’s Handbook. 
ovate ; spire obtuse, but much more prominent than 
in Helix; mouth oval; umbilicus very small. 
Tentacles shorter than in Helix. | 
19. Pupa, Lam.—Shell cylindrical or oblong, with 
many narrow whorls ; mouth oval or lunate, generally 
toothed within; peristome incomplete, thickened, 
reflected ; umbilicus very minute. 
20. Vertigo, Miill—Shell subcylindrical, with 
closely pressed, gradually enlarging whorls; mouth 
more or less angular, generally toothed internally ; 
umbilicus minute. Resembles Pupa, but differs in 
having the ventral tentacles wanting, and in having 
the peristome thinner. 
21. Balia, Prideaux.— Shell sinistral, elongated, 
thin ; mouth ovate, sometimes with a denticle on the 
base of the penultimate whorl; peristome thin; 
umbilicus narrow. 
22. Clausilia, Drap.—Shell sinistral, fusiform ; 
mouth pyriform or elliptical and toothed, furnished 
with a clausilium* ; umbilicus very small. 
23. Cochlicopa, Ferrussac.—Shell oblong or 
oblong-oval, very glossy, transparent; ‘mouth pyri- 
form ; outer lip thickened but not reflected. 
24. Achatina, Lam.—Shell cylindrical, smooth, 
* The clausilium is a shelly plate attached to the columella by 
an elastic ligament about half a whorl from the mouth, and may 
be best seen by breaking away the outer part of the body whorl. 
It serves the same function as an operculum, but it is not, as in 
that structure, fastened to the animal. When the animal extends 
itself out of the shell the clausilium is pushed against the 
columella, and when it withdraws, the clausilium flies backwards 
on account of the elasticity of its ligament, and closes the mouth 
of the shell. 
