VI. INTRODUCTION. 



point out species that could possibly be confused, 

 noting their characteristic points in contradistinction 

 to those of their nearest allies ; we have also generally 

 given not only the locality, but also the circumstances 

 under which each may be found, together with other 

 matter which the experience of several years of col- 

 lecting, has enabled us to furnish. To the many 

 localities we have gathered from various works, we 

 have added a number which now appear for the first 

 time in print, these, we hope, will prove a valuable 

 addition. 



It will be noticed that most of our British species 

 are widely distributed ; in almost any district, a radius 

 of a few miles, will supply about three-fourths of the 

 whole number ; so that any one, without assistance or 

 exchange, can possess himself of a tolerably large 

 collection. A few, however, seem confined to the 

 Southern and Midland Counties, while one or two 

 are seldom found except in the North : among the 

 former are Assiminia Grayana, Testacella halio- 

 toidea, Helix aperta, Helix pomatia, Helix pisana, 

 Helix Carthusiana, Helix obvoluta, Helix revelata, 

 Bulimus acutus, Bulimus Lachamensis , Clausilia 

 biplicata, and Succinea oblonga ; among the latter are 

 Zonites excavatus, Zonites purus, Helix hybrida, 

 Helix sericea, Helix fusca, Helix limbata, Clausilia 

 dubia, Pupa Anglica, Limnceus Burnetti, Plan- 

 orbis nautileus, and Acme lineata. There can be 

 little doubt that Geological formation plays an im- 

 portant part in the distribution of land shells, and 

 for this reason, probably, the southern part of our 

 island produces many species which are seldom, some 

 never, found further north. This is principally owing 



