04 PREFACE. 
with Mr. Say, lie is indebted for much valuable 
information respecting this class of animals, which 
has been the especial object of his attention. It 
is a cause of regret that he should not have per- 
severed in a design, conceived several years since, 
of publishing a work on the same general plan 
as the present, for the judicious execution of 
which he is peculiarly well qualified, both by 
study and observation. To Professor C. B. Ad- 
ams, of Middlebury College, Vermont, he owes 
the loan of his entire collection of his American 
terrestrial mollusks, which have been of impor- 
tant sendee in the comparison and diagnosis of 
species, and for many facts concerning these ob- 
served by him in Vermont. To S. S. Ilaldeman, 
of Columbia, Penn., he is under obligations for 
specimens collected by him during a journey 
through the southern and south-western States, 
and for much information respecting the distribu- 
tion of species. To John G. Anthony, Esq., of 
Cincinnati, Ohio, for valuable aid and many facts, 
derived from his own observation, concerning the 
species found in the neighborhood of that city. 
To J. Hamilton Coupcr, Esq., of Hopeton, near 
Darien, Georgia, for his obliging attention in 
