SOURCES OF THE BOREAL FAUNAS OF SHASTA AND OF THE 
SIERRA AND THE CASCADES. 
The boreal animals and plants of the Sierra-Cascade system as a 
whole are not yet well enough known to admit of positive statements 
as to the number of species or the details of their distribution. Hence 
a complete study of their distribution with reference to the geographic 
source of origin of the various specific types is 1ot possible. Never- 
theless, enough has been learned to point to some very interesting 
conclusions. 
It has been already shown that the boreal fauna and flora of Shasta 
form a part of the fauna and flora of the Sierra-Cascade system; that 
70 percent of the exclusively boreal mammals of Shasta are common 
to both ranges; and that of the remainder, 80 percent are common to 
the Sierra. It is obvious therefore that, so far as mammals are con- 
cerned, Shasta may be considered a part of the Sierra (see p. 71). 
Fifty-eight boreal! species of mammals are known from the Sierra 
and the Cascades. Of these, 31 (54 percent) are common to both ranges, 
11 (19 percent) are restricted to the Sierra, and 16 (28 percent) to the 
Cascades. 
Of the 58 boreal species of mammals Known to inhabit the Sierra- 
Cascade system not a single genus or subgenus is peculiar, though the 
genera Aplodontia and Neurotrichus and the subgenus Atophyrar are 
restricted to the northwest coast region. With species the case is very 
different, for 23 of the 58 species (40 percent) are peculiar to the 
Sierra-Cascades; but even of these only 10 ditfer sufticiently from near 
relatives elsewhere to be considered distinct specitic types. Of the 58 
species whose relationships are so obvious that there can be no doubt 
as to their affinities and origin, 5 (9 percent) come from mountains 
farther north (in British Columbia, some ranging into southeastern 
Alaska), 8 (14 percent) are of general transcontinental boreal distri- 
bution, 16 (28 percent) are characteristic of the humid west or north- 
west coast region, 19 (33 percent) are identical with or closely related 
to species living in the Rocky Mountains, and 10 (17 percent) are dis- 
tinctive superspecitic types restricted to the Sierra-Cascade system. 
If, instead of treating the Sierra-Cascade species collectively, we 
group them with reference to the particular part of the mountains they 
inhabit, putting the Cascade species (those north of Klamath Gap) in 
1Our collections from the Cascades have not yet been worked up, and it is proba- 
ble that several species will be added to this number. 
sO 
