24 PREFACE. 



with Mr. Say, he 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 service in the comparison and diagnosis of 

 species, and for many facts concerning these ob- 

 served by him in Vermont. To S. S. Haldeman, 

 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 Couper, Esq., of Hopeton, near 

 Darien, Georgia, for his obliging attention in 



