550 UNITED STATES GEOLOGICAL SURVEY OP THE TERRITORIES. 



3. CAMiENA, Albers. 



Shell varying from subturbinate to more or less depressed- 

 subglobose, umbilicated ; spire obtuse, moderately prominent; last 

 turn often angulated ; peristome thin or a little thickened, and 

 expanded with contiguous margins, and base expanded or reflexed. — 

 {Helix asperella, Pfr.) 

 From the foregoing, it will be seen that I adopt this genus and its sec- 

 tions almost precisely as used by the Messrs. H. and A. Adams in their 

 work on the Genera of Recent Mollusca. This, however, is not done from 

 an entire conviction that no better arrangement could be devised, but because 

 I prefer to follow reliable authority, in the absence of the necessary material 

 and time to enter upon an especial study of a great family of shells, which, 

 although immensely developed at the present time, played a comparatively 

 unimportant part among extinct forms ; while, even of the latter, I have but 

 few species to dispose of. 



It should be stated, however, here, that very widely different views in 

 regard to the limits of this genus are entertained among high authorities on 

 recent Conchology. This will be the better understood when it is stated 

 that, while H. and A. Adams only admit the three sections already mentioned, 

 Albers, who has devoted especial attention to the study of this and allied 

 groups, includes as sections or subgenera under the genus Helix alone, an 

 almost interminable list of about eighty-eight subordinate groups, designated 

 by as many different names. Without pretending, however, to have devoted 

 much time to the study of the existing forms of this group, I would merely 

 state that it seems more philosophical, and more in accordance with the 

 views of the best systematists in other departments of natural history, as 

 well as much more convenient, to treat a considerable portion of the groups 

 included as sections of this genus by Albers, as separate genera and sections 

 of the same, more nearly in accordance with the arrangement adopted by H. 

 and A. Adams. This lias already been done by Professor Morse, Mr. Tryon, 

 and, to a less extent, by some others, in classifying American types. 



In "regard to which particular one of the allied groups should inherit the 

 old generic name Helix, or, at any rate, which should be regarded as the 

 typical section of this genus, some differences of opinion exist. As originally 

 used by Linnaeus in 175S, the genus can hardly be said to have had any 



