SNAILS AND SLUGS. 



643 



Fig. 21. 



CLAUSILIA, 



showing 



clausium(c)in 



position. 



whorl. The largest species attains 7 in. in length, and lays an egg as large 

 as a pigeon's, with a calcareous shell. Stenogyra has a very long and narrow, 

 many-whorled, glossy shell ; some species are nearly an inch in length. 

 Cfficillianella is very small and lives underground. It is, as its name implies, 

 blind. One species occurs in England. 



The PUPID^ have many-whorled (more or less cylindrical) spiral shells, 

 often strongly striated and frequently sinistral. 



The genus Pupa, the chrysalis-shells, is represented in 

 Britain, as also is Clausilia, in which the shell is very long 

 and sinistral. The latter is remarkable for possessing a 

 curious little valve, the clausium, which is attached within 

 the shell by a spiral elastic stalk to the columella, and closes 

 automatically behind the animal when it retires (Fig. 21). 



The CYLINDRELLHLE, which are confined to America and 

 the West Indies, have exceedingly long, many-whorled shells, 

 with circular aperture : the last whorl often stands out from 

 the rest. 



The BULIMULID.E occur in America, Southern Asia, and 

 Polynesia. With the exception of the slug-like genus 

 Peitella, they have external high-spired shells. 



The ORTITALICID.E are an American family, whose single 

 genus Orthalicus has a shell in external shape resembling that 

 of Bidimulus. 



The HELICID.E comprise an enormous number of forms : High-spired 

 shells as in the genus Bulimus, which is confined to South America and the 

 West Indies; or as in the gaudily-painted shells of the Philippine genus 

 Helicostyla and our own Cochlvella ; shells with short spire or no spire at 

 all, as in the big genus Helix, of which the garden snail is an example. 



The family THYROPHORELLID^E has 

 been created to receive one small species, 

 Thyrophorella Thomensis (Fig. 22), from 

 the Island of St. Thomas, Gulf of Guinea. 



The unique feature about the shell, 

 which is a flat, spiral one, consists in the 

 prolongation of the upper half of the 

 peristome beyond the aperture and the A 

 formation of a hinge allowing this pro- 

 jection to close over the mouth and thus 

 act like an operculum when the animal 

 retires. 



The ARIONID^E are slugs whose shell 

 is represented by a few calcareous grains 

 beneath the mantle. The big black slug 

 Avion ater is a type. 



The PHILOMYCID^E are shell-less slugs found in North and Central America, 

 Eastern Asia, and Java. 



The ENDODONTID^E have flatly-coiled shells, generally ribbed and marked 

 with little red patches. The common little Pyramidula rotundata is a 

 British example. 



The LIMACID^ are slugs with small, internal, shelly plate. The majority 

 of the British slugs belong to this group. 



The ZONITID^E have external shells, often very thin and shining. The 



B 



Fig. 22. THYROPHORKLLA. 



A, The animal crawling 1 . B, The shell seen 



edgewise. C, Do. seen from beneath. 



