: LYMN IDA OF NORTH AMERICA. 307 
The above table shows that there is some variation in the measure- 
ments of the different organs. The genitalia of palustris differ from 
those of the smaller Lymnzas (Galba) in the form of the prostate, 
which is ovate in Galba while in Stagnicola it is squarely rounded at 
the anterior end and gradually tapers toward the posterior end. athe 
penis is also thicker and larger in Stagnicola. 
The size and number of eggs in the egg-capsules of Galba palustris 
are as follows: 
Length. Width. Eggs. 
12.50 mill. 3.50 mill. 82 Illinois. 
13t00n 350m ee 68 7 
1600) 5 4.50 “ 50 Colorado. 
TLE) = ACS Oma 64 ‘< 
illo) Ala{0) 26 us 
RANGE (Figure 33): Circumboreal. Northern Asia and Europe. 
North America from the Atlantic to the Pacific Ocean, and from 
Alaska south to New Mexico. 
Palustris probably inhabits nearly the whole of North America 
from the Arctic Circle to southern California and New Mexico. It 
appears to be absent from the Lower Austral (Austro-riparian divi- 
sion). It may be said to be characteristic of the Boreal and Tran- 
sition life zones, from whence it has penetrated into the Upper Austral 
life zone. Its absence from Labrador, Ungava and the northern part 
of this region may be accounted for by lack of records. Although 
reported from these regions by Dall (Alaska Moll., p. 7 6), no speci- 
mens from these areas have been examined by the writer, nor have 
any definite rcords been seen. It is possible that its place in this region, 
as well as in Greenland, is taken by Galba vahlii. West and north- 
west of Hudson Bay it is common and widely distributed. Its hypso- 
metric distribution extends to 9000 feet in Colorado, 7760 feet in 
southern California, and 10,000 feet in the Uinta Mountains, Utah. 
Comparing the range of palustris with the drainage regions, we 
find it absent from the Labradorian, Alaskan, Carolinian, Lower Mis- 
sissippian and Central American regions. It enters the Rio Grandian. 
The neighborhood of the 40th parallel marks the southern boundary 
in this region, excepting a small portion of Ilinois. In the west, 
palustris extends almost to the 30th parallel, the altitude providing the 
temperate. climate of the northern portion of the Mississippi Valley. 
The general northwesterly extension of the distribution indicates ap- 
parently the origin of the species in America, it being an emigrant 
from Asia via Bering Strait. Additional records will doubtless estab- 
lish an unbroken route from the Arctic shores of Alaska to the Great 
