FAMILY C0L1MACEA. 35 



acicular species is the northernmost member of an intertropical 

 form of which there are two hundred and fifty species, of varying 

 groups, all characterized, however, by an involute truncation of the 

 columella of the shell. 



The remaining genera of Colimacea are Clausilia, Balea, Pupa, 

 and Vertigo, numbering about five hundred and fifty species, of 

 which eighteen are British. Of Clausilia we have only four species, 

 although it is an essentially European type. As many as three 

 hundred and twenty species are known, nine-tenths of which are 

 natives of Austria, Hungary, and the islands of the Grecian Archipe- 

 lago ; and the remainder range, in a gracefully developed state, in 

 the more distant kingdoms of the East. The shell of Clausilia is 

 always convoluted sinistrally, peculiarly constricted in the neck of 

 the last whorl, and the animal possesses the faculty of closing itself 

 in by means of a spoon-shaped appendage attached by an elastic 

 filament to the columella. Balea is a European snail, having a 

 turreted sinistral shell, without any exotic analogue. Pupa and 

 Vertigo, concluding the series, were formerly imited, but they are 

 now shown to be distinct. In Pupa the lower tentacles begin to 

 lessen and are reduced to mere protuberances. In Vertigo they 

 disappear altogether, and the animal, agreeably with its change of 

 habit in dwelling chiefly on the banks of lakes and rivers, partakes 

 in this respect of the character of the water snails. The species of 

 Vertigo are without exception smaller than any Pupa. We have only 

 four Pupce in Britain, to a hundred and fifty foreign species, nearly 

 half of which are European. About forty belong to other more 

 tropical Eastern countries, and the remainder to the New World, 

 not less than thirty of them being stationed at the West Indies and 

 the neighbouring mainland. Of Vertigo we have nine interesting 

 minute species in Britain. The extra-British species of this genus 

 are about seventy in number, agreeing pretty nearly in their distri- 

 bution with the Pupce, excepting that there are fewer in proportion 

 in the West Indies, and more in the United States. 



The British genera of Colimacea are : — 



1. Vitrina. Animal carrying a lightly whorled, glassy shell, over 



which a lobe of the mantle is reflected, and in front has a 

 fleshy shield with the respiratory orifice behind it to the 

 right. Shell of three imperforate pellucid whorls. 



2. Succinea. Animal carrying a thin, submembranaceous shell, 



head broad and obtuse, lower tentacles short. Shell oblong- 



i) 2 



