72 NORTH AMERICAN FAUNA, (xo. 16. 
from the Cascades; 15 are common to Shasta and the Cascades but 
are not known from the Sierra; and 8 are restricted to Shasta. 
Three mammals, 5 birds, and 68 plants are believed to be restricted 
to the Hudsonian and Alpine zones. Of these, 2 mammals, 3 birds, 
and 30 plants are common to the Sierra and the Cascades; one mam- 
mal, 1 bird, and 18 plants are common to Shasta and the Sierra but 
are not known from the Cascades; and no mammal, 1 bird, and 12 
plants are common to Shasta and the Cascades, but are not known 
from the Sierra. Five Hudsonian Alpine plants from Shasta are not 
known from either the Sierra or the Cascades. 
These comparisons show: 
(1) That of the boreai species known from Shasta, including those 
which range down into the Transition zone, 87 percent of the birds, 
72 percent of the mammals, and only 50 percent of the plants are 
common to the Sierra and the Cascades. 
(2) That of the exclusively boreal species known from Shasta, 85 per- 
cent of the birds, 70 percent of the mammals, and 46 percent of the 
plants are common to the Sierra and the Cascades. 
(3) That of the exclusively Hudsonian and Alpine species known 
from Shasta, 60 percent of the birds, 67 percent of the mammals, and 
d4 percemt of the plants are common to the Sierra and the Cascades, 
(4) That in each instance, as would be expected, the percentage of 
Species common to the two ranges is greater in the case of those rang- 
ing down into the Transition zone than in those restricted to the Boreal, 
for the obvious reason that geographically the Boreal belt is broken by 
broad gaps, while the Transition zone is practically continuous. 
(5) That of tbe birds, mammals, and plants of Shasta, birds have by 
far the largest percentage of species common to the Sierra and the 
Cascades, mammals next, and plants least of all. This corresponds 
with the relative powers of dispersion possessed by these groups. 
Arrauged primarily by groups instead of zone limits, it appears that 
the percentages of Shasta birds common to the Sierra and the Cascades 
are as follows: Of boreal species, including those which range down 
into the Transition zone, 87 percent; of species restricted to the Boreal 
zones, 85 percent; of species restricted to the Hudsonian and Alpine 
zones, 60 percent. 
The percentages of Shasta mammals common to the Sierra and the 
Cascades are: Of boreal species, including those which range down into 
the Transition zone, 72 percent; of species restricted to the Boreal 
zones, 70 percent; of species restricted to the Hudsonian and Alpine 
zones, 67 percent.' 
The percentages of Shasta plants common to the Sierra and the Cas- 
cades are: Of boreal species, including those which range down into 
the Transition zone, 49 percent; of species restricted to the Loreal 
'The nunber of Iudsonian-Alpine species is too small to give this percentage 
much value. 
