148 



LAND AND FRESH-WATER SHELLS OF N. A. [PART 1. 



The specimens selected for figuring show the variation in size 

 of the species. The smaller form (from near Philadelphia) is 

 often found imperforate and toothless. 



Jaw long, narrow, sligktly arcuate, with thirteen stout ribs on 

 both anterior and posterior surface, denticulating the cutting 

 margin. 



Teeth of the lingual membrane obtusely conical, surmounted 

 by a long, sharp apex. 



Fig. 252. 



Liugual dentition of Helix thyroides. [Leidy.] 



Helix 1)liccilleieta, Gould. — Shell usually perforate, globose-conic, 

 tDOie or less elevated, rather thin, shining, pale yellowish-green, surface 

 regularly and delicately furrowed by the striae of growth ; whirls five or a 

 little more, rounded, and separated by a well-impressed suture ; base con- 

 Fig. 253. 



Helix hucculenta. 



vex ; aperture rounded ; peristome forming nearly two-thirds of a circle, 

 rather broadly retlexed, white, somewhat llesh-colored behind^ not com- 

 pletely covering a small umbilical perforation, sometimes entirely covering 

 it; parietal wall sometimes bears a small white tooth at the middle, but 

 oftener not. Greater diam. \^\, lesser 15^; height lOi mill. 



