INTRODtfC.] 
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 Regions, 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 modem 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. 
