14: Remarks on Classifications of 



species determined by Albers to be in Triodopsis. H. hippo- 

 crejpis (with the tubercle as in pustula\ having a reflexed hook 

 far within the aperture, connects the group in which the latter 

 is placed with that embracing auriculata and its allies. 



The value, as generic characters, of the fulcrum and tubercle 

 above described (existing in North American species only, so 

 far as I am informed), remains to be decided. 



No scientific arrangement of the North American Helices 

 can, however, be framed until more is known of the animals. Dr. 

 Gray {Aiin. and Mag. of Nat. Hist. I. c. 268) remarks on " the 

 impossibility of defining with accuracy and certainty, from the 

 examination of the shell alone, the genus, family, or even order 

 to which a Mollusk may belong ;" adding that, " shells similar 

 in external appearance and character have animals of different 

 conformation and habits." In this connexion I would mention 

 that Mr. W. G. Binney and m^^self are now aiding in an investi- 

 gation of the jaws and lingual teeth of as many North American 

 species as possible, of which figures will be published in a work 

 now being prepared for the Smithsonian Institution. 



The chief object of this paper being to facilitate and encou- 

 rage inquiry by affording information, I conclude by annexing 

 to the Catalogue copies of the descriptions, given by Albers, of 

 the principal Genera and Subgenera in which he arranges the 

 American species of Helix herein mentioned. 



