4 INTRODUCTION. 



the subject, and reference has been made to snch of 

 their observations as have appeared to be of sufficient 

 importance to find a place in a work which is in- 

 tended only as a manual for the student. One ani- 

 mal of each of the more typical genera of each of the 

 families has been figured, and new plates have been 

 added, containing the species not before figured, 

 together with figures and details of some of the 

 smaller species, which were not executed so well as 

 might have been wished in the preceding edition. 



Wishing to make the work really what its title re- 

 presents it, the species described are restricted to those 

 which appear to be truly native, and only the two fol- 

 lowing, viz. — 



Testacella haliotoidea, t. 3. f. 19., and 

 Driessina polymorpha, 

 have been admitted among those which are supposed 

 to have been introduced in modern times. These have 

 been admitted, because they have become truly natu- 

 ralised, and propagate themselves in our climate in the 

 open air. Indeed it is doubtful whether the first of 

 them may not be as truly native as several other species 

 commonly considered so ; such as, Helix Pomatia, H. 

 holosericecL) H. lijnbata, H. Carthusiaiia, and H. Pisana. 

 Several other species were recorded and described in the 

 first edition of this work, which have been introduced 

 with foreign plants, either buried in the mould, or on 

 the plants themselves, or which have most probably been 

 brought to this country in the egg state. These are not 

 truly acclimatised, and only propagate their species 

 when they are kept in stoves or hot-houses ; they can 

 therefore have no pretension to be considered as na- 

 tives : among them must be recorded, the 



