1918 | Taylor: Revision of the Rodent Genus Aplodontia 445 
the other. The inner and outer prominences of the broad angular 
process of the jaw are differently outlined in different specimens, 
and the ridge extending from the inner prominence of the angular 
process exteriorly on the jaw to bound the masseteri¢ fossa anteriorly 
is comparatively well developed in certain specimens, whereas in 
others it is interrupted by a smooth space. 
4. Motr AND SEASONAL VARIATION 
There is but one molt annually in Aplodontia. Pelage renewal 
begins in July and August, rarely as early as June, and continues 
for two or three months. There is no hard and fast manner of molt- 
ing. The hair usually begins coming in on the sides posteriorly and 
on the back of the head and neck about the same time. From these 
centers the molt spreads until the new pelage covers the body, the 
hair of the shoulders and rump being the last to be renewed dorsally. 
In some examples the molt proceeds somewhat irregularly. The molt 
of the underparts lags behind that of the upperparts. Additional 
details as to molt are mentioned in the accounts of species and sub- 
species. 
The new pelage is longer and sometimes slightly different in color- 
ation from the worn pelage it replaces. Thus in Aplodontia rufa 
pacifica, the fresh pelage is more richly colored than the worn pelage ; 
in A. r. californica, it is a trifle browner; and in A. r. phaea, it is a 
little more intensely colored. Differences in coloration and general 
appearance are small, however, and in several forms of Aplodontia, 
as at present represented in the collections examined, cannot be shown 
to exist at all. 
5. GmoGRAPHIC VARIATION 
Geographic variation, like time variation, is comparatively slight 
in the genus Aplodontia. The forms are so little differentiated that 
variation geographically is often obscured by individual variation. 
All of the described forms may with entire propriety be referred to 
a single species. 
Mountain forms are larger as a rule than nearby lowland or 
coastal forms. Thus Aplodontia rufa columbiana of the mountains 
of Hope District, British Columbia, tends to be larger than A. r. rufa 
of the Puget Sound region; in lke manner raimiert from Mount 
