34 BRITISH MOLLUSKS. 



much, unlike that of Vitrina. Datcdehardia is a native of Central 

 and Southern Europe and Syria. 



Another genus of Colimacea is one of which at least a hundred 

 and forty species have been described from different parts of the 

 world, three of them British, Succinea; they are mostly natives 

 of the western hemisphere, where Vitrina is unknown, except by a 

 single small species in the United States, descended probably from 

 an exported European individual. Succinea has a light, transparent, 

 fusiformly coiled shell, largely inflated, and of a delicate amber 

 colour. The next genus in the series, Zonites, has a regular helici- 

 form shell, colourless and poHshed, arising from the action of a par- 

 tially reflected lobe of the mantle. We have eight well-defined 

 species in Britain ; the foreign species, of which some thirty or forty 

 have been noted, are as yet but imperfectly eliminated from Helix. 



Of Helix, the most numerous and widely distributed of all Coli- 

 macea, upwards of two thousand species have been described. They 

 inhabit all lands and all elevations within the range of molluscan 

 life. The British Helices are twenty-four in number, mostly small. 

 A few are pre-eminent in size and colour, and almost rival tropi- 

 cal species in brilliancy and marking. The fifth genus of the family, 

 Bulimus, scarcely differs from Helix in the soft parts, but the ani- 

 mal is more arboreal in habit, and has a more elongately convo- 

 luted shell, with a more restricted range of habitation. Nine hun- 

 dred species have been described in all, chiefly natives of the inter- 

 tropical regions of both hemispheres, and some of them with shells 

 of quite colossal dimensions. We have only three small species in 

 Britain. In the United States there is no Bulimus within fifteen 

 degrees of the same latitude. The three genera which follow, Zua, 

 Azeca, and Acliatina, represented in Britain by a single species 

 each, are included by M. Moquin-Tandon under Bulimus. They 

 are, it appears to me, very distinct. Zua has a highly polished, 

 vitrified shell, and a geographical distribution peculiarly its own, 

 the most extended both in space and elevation of all land mollusks. 

 The single known species, for there is no satisfactory evidence of 

 the existence of more than oue, ranges throughout Europe and 

 Northern and Central Asia, reaching from Siberia to Cashmere and 

 Thibet, and it appears indigenous in most of the United States. 

 Azeca, of which all the described species are probably referable to 

 one, is peculiar in form, contracted and toothed in the aperture. 

 The extra-British distribution of this genus is confined to Central 

 Europe. Acliatina belongs to a different category. Our minute 



