OF NORTH AMERICA. 65 



sonomansis. reflexa walkeri. emarginata angulata. 



hendersoni. rencxa hemphilliana. emarginata wisconsinensis. 



caperata. exilis. emarginata canadensis. 



umbilicata. kirtlandiana. emarginata ontariensis. 



cyclostoma. danielsi. contracta. 



parva. firoxima. pilsbryana. 



parva sterkii. proxima rowelli. montana. 



owascoensis. leai. oronensis. 



dalli. tryonii. binneyi. 



pilsbryi. apicina. 



humilis. apicina solida. 



humilis modicella. hinklcyi. 



randolphi. 



SPECIES AND VARIETIES SOUTH OF 38. 



stagnalis appressa. bulimoides cassi. obrussa exigua. 



lepida. caperata. galbana. 



columella. parva. palustris. 



columella chalybea. parva sterkii. proxima. 



columella championi. dalli. proxima rowelli. 



francisca. humilis. tryonii. 



cubensis. humilis modicella. leai. 



cubensis aspirans. ferruginea. traskii. 



bulimoides. obrussa. gabbii. 

 bulimoides techella. 

 bulimoides cockerelli. 



SPECIES AND VARIETIES SOUTH OF 30. 



columella championi. cubensis aspirans. attenuata. 



cubensis. bulimoides techella. 



francisca. obrussa. 



SPECIES AND VARIETIES SOUTH OF 20. 



cubensis. cubensis aspirans. columella championi. 



The 105th degree of west longitude (exclusive of Mexico, Central 

 America and the West Indies) may be taken roughly as a dividing 

 line between a western and an eastern Lymnaeid fauna. As a matter 

 of fact, the 105 marks the eastern boundary of this faunal region 

 from the 35th to the 42nd parallel, from whence the boundary is 

 marked by the Rocky Mountain Chain, which extends northwesterly 

 through British America and Alaska. 44 species and varieties have 

 been recorded west, and 70 species and varieties east of this dividing 

 line. 17 species and varieties are common to both. 26 are thus pe- 

 culiar to the western, and 53 to the eastern region. In the Mississippi 

 Valley south of the 42nd parallel, the region between the 100th and 

 the 105th degrees is almost void of members of this family, only 9 

 species and varieties being recorded. This is the great plains area, 

 which is probably unfavorable to the usual luxuriant development of a 

 Lymnseirl fauna. 



