PREFACE. 
The great attention paid to the British land and 
fresh-water shells by Montagu ; by my late friend 
and teacher in zoology, Dr. Leach; and more recently 
by Mr. Jeffreys, Mr. Jenyns, and Mr. Alder (more 
especially the latter), has left me little else to do, in 
revising this edition, than to embody their observa- 
tions. This is the more peculiarly the case, inasmuch 
as they all, in a great measure, worked from the 
collection now under my charge, which contains the 
materials used by Dr. Leach in preparing his work 
on British Mollusca, and, among the rest, the various 
specimens which I had myself collected when actively 
engaged in the study of our British species. It is 
right, however, to add, that, before adopting the 
remarks of these authors, I have, in every instance 
where it was in my power (and that was almost 
universally), verified the facts myself ; and therefore, 
although I have used their words from a desire to 
do justice to their labours, the conclusions are most 
frequently equally my own. 
