92 HELICHLE. 



such as H. calif orniensis, nickliniana, tudiculata, and 

 buffoniana. They are large, thin, vesicular shells, 

 banded, and with the surface more or less indented. 



Another natural group may be instituted having H. 

 fuliginosa for its type, associated with H. lucubrata, 

 inornata, demissa, and subplana ; near these, if not 

 strictly united with them, is another group composed of 

 H. arborea, electrina, Ottonis, and indentata. They 

 are, in both cases, of a lenticular form, and remarkable 

 for their smooth and glistening surface and delicate 

 structure. They are closely allied in characters to the 

 genus Nanina, and belong to Ferussac's genus Helicella. 

 The first group is mostly confined to the Southern and 

 South-western States, while those of the second group 

 are very widely distributed. 



H. yularis, lasmodon, and suppressa compose another 

 small group, similar to the preceding in form and in 

 the polish of their surface, but peculiar on account of 

 a curious lamination within the throat of the aperture. 

 They are found only in the middle Atlantic States and 

 the region of Tennessee. 



H. alternata, perspectiva, striatella, and cumberland- 

 iana form another group, remarkable for their discoidal 

 form, broad umbilical concavity, and especially for their 

 lyrately ribbed surface. 



Helix ligera and intertexta, from the region of the 

 Ohio River, are naturally allied to each other. 



Thus we see that many of the groups formed by allied- 

 species are also quite local in their distribution, while 



