McGrew (1941) said that the mountain beaver presents: a picture 
exactly the opposite of that required by the Matthewsian hypothesis. 
He also said that the present range of the mountain beaver is appar- 
ently near the center of origin and distribution of the family 
Aplodontidae. Furthermore, he suggested that the distribution of 
the mountain beaver cannot be accounted for by climatic or environ-~ 
mental change at the center of dispersal because environmental con-~ 
ditions along the Pacific Coast might have been quite stable during 
Tertiary time, or at least stable enough to allow the mountain beaver 
to maintain its range with relatively little structural modification. 
McGrew said that those that migrated did so either because of popula- 
tion pressure or the inherent tendency of all animal life to expand, 
Those that were not successful in adapting to new environment became 
extinct, or their range became restricted. 
RACES AND RANGE 
Figure 2 illustrates the present distribution of the mountain 
beaver. Taylor (1918) recognized wide individual variation, as well 
as considerable geographical variation, Thus, mountain forms are 
generally larger than nearby lowland or coastal forms. The most 
strikingly colored form is the geographically isolated Aplodontia 
rufa nigra of Point Arena, California. 
Taylor (1918) revised the 13 races of the mountain beaver and 
listed nine, four of which occurred in the State of Washington. 
Finley (1941) also recognized four races in Washington. Dalquest 
and Scheffer (1945) concluded as a result of their investigation on 
- specimens from the Biological Survey Collection, Washington, D.C., 
and on specimens in the Museum of Vertebrate Zoology, that there were 
only fwo recognizable races in Washington: rufa in western Washington 
and rainieri in the Cascades. Miller and Kellogg (1955) and Hall and 
Kelson (1959) also recognized these two races in Washington. The type 
locality and distribution of the seven races of the mountain beaver 
are listed in appendix l. 
DESCRIPTION 
The material under External Characters and Pelage was based on the 
examination of specimens in the National Museum and specimens obtained 
from Olympia, Wash., with references drawn from Coues (1877b). 
External Characters 
The general body conformation of the mountain beaver is stout, 
compact, and cylindricoid. The average adult weighs about 2-1/2 pounds 
and measures slightly more than a foot, resembling a tailless muskrat 
(Ondatra zibethica). 
