of North American llelicidoe. 119 



A number of the North American Helices have, besides the 

 teeth, the process first noticed by Lea (Obs. Y., 60), as a " pillar 

 or additional column, placed like a fulcrum (buttress) in the 

 interior, against the wall of the ordinary column, at the distance 

 of a fifth to a third of a revolution of the whorl from the aper- 

 ture." Lea first observed this in II. spinosa^ and subsequently 

 in seven other species. He remarks that the fulcrum " will be 

 found in some species to be a simple round column soldered to 

 the paries of the main column ; in others a compressed or flat- 

 tened column extending into the cavity of the whorl." The 

 purpose, he adds, " of this fulcrum or buttress is very evidently 

 instituted for the greater strength of the ultimate whorl, which, 

 being very much enlarged, seems in some of these more deli- 

 cate species to require additional support." 



With regard to the particular use of this curious appendage, 

 which exists only, so far as I know, in shells having the aperture 

 contracted by teeth, I suggest that it acts literally as a, fulcrum, 

 in connexion with which the muscles of the animal have 

 increased leverage power to draw back its protruded body into 

 the shell, in the performance of which operation the teeth are 

 obstacles, — yet many toothed shells are without this process. 



In repaired individuals of II. monodon, not only is a new 

 parietal tooth added, as above mentioned, but the fulcrum is 

 also reconstructed in its proper position with respect to the new 

 aperture. The locality of the old fulcrum is indicated by a 

 callus,— whether it was broken off or removed by the animal I 

 am unable to determine. 



The following, framed from personal observation of specimens 

 in my cabinet, presents an arrangement of the species of Helix 

 of Eastern North America, based on the number of teeth, dis- 

 tinguishing those which have the fulcrum, and also the cha- 

 racter of the lip — whether simple or reflected. 



A. Lip simple — no fulcrum. 



1. One tooth within at base of ajyerture. 

 H. perspectiva Say. 



