178. With six whorls; height usually more than threcfourths width; 3/^" to 



1"; central states 



Mesodon (Mesodoyi) elevatus (Say) 

 With less than six whorls; height usually less 179. 



179. Height about 60 ^c of width; about 1%"; east of the Mississippi River 



Triodopsis (Jsleohelix) alholahns (Say) White-lipped Wood 

 Snail 

 Height about 70% of width; about 1"; eastern and central states 

 Mesodon (Mesodon) z-aletus (Binney) 



180. Toothless or with one tooth on the parietal wall 181. 

 Aperture usually with one tooth on the parietal wall and with one or 



two teeth on the lip 185. 



181. West Coast Shells 182. 

 In the eastern and central states 183. 



182. Umbilicus almost covered by the reflected lip; about Yg'; California 



Vespericola megasoma (''Dalb' Pilsbry) 

 Umbilicus slightly covered by the reflected lip; about Vs"; Pacific states 

 Vespericola columhiana (Lea) 



183. Umbilicus wide, about one-fifth the diameter of the shell; lip usually with 



a thickened area within the base of the aperture; with or without re- 

 volving bands of color; 1" to 1%" 



Allogona (Allogona) profunda (Say) 

 Lip turned back over a small umbilicus; lip without basal callus; plain 

 colored 184. 



184. Reflected lip wide and flat; with or without a tooth on the parietal wall; 



about 1" 



Mesodon (Mesodon) thyroidus (Say) White-lipped Wood Snail 

 Reflected lip narrower and more rounded; no tooth on the parietal wall; 

 umbilicus smaller than in the preceding species; less than %" 

 Mesodon (Mesodon) clausus (Say) 



185. With one tooth on the lip at the base of the aperture; about l"; eastern 



and central states 



Mesodon (Appalachina) sayanus (Pilsbry) 

 (Polygyra sayi (Binney) ) 

 Typically wath two teeth on the lip 186. 



186. Tooth on parietal wall long and narrow, joined or almost so with the 



axial end of the lip; eastern and east-central states 187. 



Tooth on parietal wall rather small; western species 188. 



187. Aperture almost closed by the teeth; about ^2'' 



Triodopsis (Triodopsis) fraudulenta (Pilsbry) 

 Aperture not so constricted; about ^2'' 



Triodopsis (Trwdopsis) tridentata (Say) 



188. Umbilicus almost covered by the reflected lip; about V2"; western states 



Trwdopsis (Cryptomastix) mullani (Bland 6? Cooper) 



135 



