448 University of California Publications in Zoology — |Vou. 17 
upper premolar four, somewhat broken) was found has been referred 
to the Upper Miocene (loc. cit., p. 171), the Cedar Mountain fauna 
being regarded as intervening in time between the Mascall Middle 
Miocene of the Middle Basin area and the Barstow Upper Miocene 
of the Mohave area. 
That both Aplodontia alerandrae and the Cedar Mountain species 
represent advanced stages of development between Allomys and 
Aplodontia seems clear. Both are nearer Aplodontia than Allomys; 
but neither one is so specialized as are the Recent forms of Aplodontia. 
There remains to be considered only Aplodontia major fossilis 
Sinclair (1905, pp. 147-148), discovered in 1902 by an expedition from 
the University of California, in the Pleistocene Potter Creek Cave, 
Shasta County, California. Comparison of the numerous remains of 
this species in the University of California Collections in Vertebrate 
Palaeontology with a large series of skulls and jaws of Aplodontia 
rufa californica, the Recent form occurring in the same general 
region, shows that the Pleistocene form is very doubtfully if at all 
distinguishable from the living species. 
2. SUMMARY AND Discussion 
It is worthy of remark that nearly all of the records of extinct 
members of the family Aplodontiidae are from the now arid territory 
east of the great Cascade-Sierra mountain system, which system, at 
the present time, marks the eastern boundary of the range of the 
genus (see map, text-fig. E). The members of the chiefly Oligocene 
genus Allomys hail from the John Day Beds of eastern Oregon, with 
one outlying undetermined species in the Rosebud Lower Miocene of 
South Dakota; Mylagaulodon comes from the top of the Upper John 
Day in eastern Oregon; Aplodontia alerandrae oceurs in the arid 
Virgin Valley and Thousand Creek beds of northern Humboldt 
County, Nevada; an Aplodontia of an unnamed new species comes 
from the Cedar Mountain region of western Nevada; and only Aplo- 
dontia major fossilis, found in the Pleistocene Potter Creek and 
Samwel caves, in the Shasta region of northern California, comes 
from the Pacific slope of the Sierran system. Apparently the range 
of the family Aplodontiidae, as well as of the genus Aplodontia, was 
formerly much greater than at present, though it must be conceded 
that very little is known of the precise relationships of the early 
aplodontids to the Recent genus, and we have little data on the west- 
ward range of members of the family in Tertiary time. 
