SOURCES OF THE BOREAL FAUNAS OF SHASTA AND OF THE 

 SIERRA AND THE CASCADES. 



The boreal animals aiul plauts of the Sierra-Cascade systeui as a 

 whole are not yet well enoagii known to admit of ])Ositive 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 not 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 10 (28 percent) to the 

 Cascades. 



Of the 58 boreal species of mammals known to inhabit the Sierra- 

 Cascade system not a single genus or snbgenus is ])eculiar, though the 

 genera Aplodontia and Neurotrichus and the subgenus Atophi/ra.r are 

 restricted to the northwest coast region. With species the case is very 

 different, for 23 of the 58 si^ecies (40 percent) are peculiar to the 

 Sierra-Cascades; but even of these only 10 differ sufticiently from near 

 relatives elsewhere to be considered distinct specific types. Of the 58 

 species Avhose relationsliips 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, 10 (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 Eocky Mountains, and 10 (17 percent) are dis- 

 tinctive superspecific 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 monntains they 

 inhabit, putting the Cascade species (those north of Klamath Cap) in 



'Our collections from the Cascades have not vet been worked up, and it is proba- 

 ble that several species will be added to this luimber. 



85 



