introduc] INTRODUCTION. 169 



than has been made use of by any previous writer. Several 

 discussions on the bearing of the facts of insect distribution, 

 will also be found under the several Eegions, in the preceding 

 part of this work. 



Terrestrial Mollusca form a group, as to the treatment of which 

 I have most misgivings ; owing to my almost entire ignorance of 

 Malacology, and the great changes recently made in the classifi- 

 cation of shells. There is also much uncertainty as to genera and 

 sub-genera, which is very puzzling to one who merely wishes to get 

 at general results. Finding it impossible to incorporate the new 

 matter with the old, or to harmonise the different classifications 

 of modern conchologists, I thought it better to confine myself to 

 the standard works of Martens and Pfeiffer, with such additions 

 of new species as I could make without fear of going far wrong. 

 In some cases I have made use of recent monographs — especially 

 on the shells of Europe, North America, the West Indian Islands, 

 and the Sandwich Islands ; and have, I venture to hope, not 

 fallen into much error in the general conclusions at which I have 

 arrived. 



