MONOGRAPH 



OP THE 



TERRESTRIAL MOLLUSCA 



OF THE 



XJnlteca. Sta^tes. 



PEEFACE. 



T'he substance of the following pages was written by me 

 some years ago for my own use, in identifying the species 

 of North American Land Shells. Having found it an import- 

 ant aid in this connection, saving me much time, trouble and 

 uncertainty, I have concluded to publish it, in the hope that 

 it will prove alike useful to others pursuing the same study. 

 To this end, the subject has been carefully reviewed, much of 

 it re-written, and all the species published to this date included. 



After a vain attempt to reconcile the prominent characters of 

 the shells with the characters of the soft parts, or animals, as 

 described by recent observers, and to divide the species ac- 

 cording to the families and sub-families which they have in- 

 stituted, I have concluded to introduce only such of these 

 divisions as will give the genera and species as nearly as pos- 

 sible in their natural sequence, founded upon Conchological 

 distinctions. 



In pursuing this course (unavoidable, on account of the 

 paucity of our knowledge of anatomical characters, and of the 

 values of these characters in classification), we less regret the 

 absence of a strictly scientific arrangement, because without 

 it we can more readily attain the object of these pages than by 



iii. 



