PREFACE. 



The great attention paid to the British land and 

 fresh-Avater shells by IMontagu ; by my late friend 

 and teacher in zoology. Dr. Leach; and more recently 

 by Mr. Jeifreys, 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, Avhich contains the 

 materials used by Dr. Leach in preparing his Avork 

 on British MoUusca, 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 

 Avhere 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 otvn. 



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