LYMN-EIDZ OF NORTH AMERICA. 65 
SONOMENSIS. reflexa walkert. emarginata angulata., 
hendersoni. refiexa hemphilliana. emarginata wisconsinensis. 
caperata. exilis. emarginata canadensis. 
umobilicata. ; kirtlandiana. emarginata ontariensis. 
cyclostoma. danielsi. contracta. 
parva. proxima. pilsbryana. 
parva sterkti. proxima rowelli. montana. 
owdascoensis. leai. oronensis. 
dalli. tryonii. binneyi. 
pilsbryt. apicina. 
humilis. apicina solida. 
humilis modicella. hinkleyt. 
randolphi. 
SPECIES AND VARIETIES SOUTH OF 38°. 
stagnalis appressa. bulimoides casst. obrussa exigua. 
lepida. caperata. galbana. 
columella. parva. palustris. 
columella chalybea. parva sterkii. proxima. 
columella championi. dalli. proxima rowelli. 
francisca. humilis. tryonti. 
cubensis. humilis modicella. leai. 
cubensis aspirans. ferruginea. traskit. 
bulimoides. obrussa. gabbii. 
bulimoides techella. 
bulimoides cockerelli. 
SPECIES AND VARIETIES SOUTH OF 30°. 
columella championt. cubensis aspirans. attenuata. 
cubensis. bulimoides techella. 
francisca. obrussa. 
SPECIES AND VARIETIES SOUTH OF 20°. 
cubensis. cubensis aspirans. columella champion. 
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 Lymneid 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 
Lymneid fauna. 
