238 BULLETIN NO.. VII. 



formly traceable, being generally present in specimens from 

 about Washington, but much stronger in those from S. Carolina 

 and Florida, in which it generally forms a strong, broad bar, 

 though sometimes obsolete." 



The amount of black i. e. the length of the black tips of the 

 coarser hairs is variable in the same locality, seasonally and 

 otherwise, 



Winter specimens are lighter than the same individuals in 

 summer, and the difference is apparently greatest to the north. 

 Our Minnesota winter specimens are very light colored. Al- 

 though there seems to be a tendency to a decrease in size 

 southward according to the usual law, it is slight and speci- 

 mens from Mexico are as large as northern individuals. The 

 local peculiarities of station seem to have a more direct influ- 

 ence than the general geographical influences. 



' ' Southern specimens generally have the ears less covered 

 han northern ones, the feet less heavily furred, and the gen- 

 eral pelage harsher and less full. Southern specimens also 

 show a tendency to decidedly longer ears than the northern 

 ones." This is in accordance with the law, an increase of 

 mean annual temperature and humidity tends to cause greater 

 development of apendicular parts. 



VAR. NUTTALLI. 



This variety expresses the law that treeless, dry regions 

 tend to diminish the intensity of coloring. "The lightest 

 specimens appear to' be those from western Wyoming, Colorado, 

 Nevada and Utah, Arizona specimens passing gradually into 

 var. arizonce." In size there is some difference, the present 

 variety being, according to Allen, about twelve per cent, smaller. 

 The proportions are the same and the difference in size has 

 usually been overestimated. Northern specimens have dense 

 soft fur and heavily -clothed ears and feet. The paleness is due 

 to a suppression of the yellowish or fulvous subterminal rather 

 than the black terminal portion of the coloring. 



VAR. ARIZONA 



is the extreme of the tendency expressed by the above but with 

 the addition of considerably elongated ears, they being one- 

 third longer than those of types of the above variety. This 

 variety was founded upon some six specimens, of which part 

 at least were young, and we await with interest the accumula- 

 tion of additional material. 



