642 THE AMERICAN NATURALIST, 
ge. Sciurus douglasii albolimébatus Allen. California chickaree. Sierra 
Nevada region of California, north into Oregon, east of the Cascades 
= Sciurus hudsonicus californicus Allen, 1890). 
gd. Sciurus douglasii mearnsi (Townsend). Mearns’s chickaree. San 
Pedro Martir Mountains, Lower California. 
10. Sciurus fremonti Aud. & Bach. Fremont’s chickaree. Mountains of 
Colorado, north to the southern border of Wyoming, and west to the 
Uinta Mountains. 
loa. Sciurus fremonti neomexicanus Allen. Taos chickaree. New 
Mexico. 
106. Sciurus fremonti mogollonensis (Mearns). Arizona chickaree. 
Mountains and higher plateaus of central Arizona. 
As shown above, the subgenus Hesperosciurus is represented 
by a single species and an additional subspecies ; the subgenus 
Neosciurus is also represented by a single species with four addi- 
tional subspecies ; the subgenus Otosciurus has a single species 
and an additional subspecies in the United States, and a second 
species in Mexico; the subgenus Parasciurus has two species 
and two additional subspecies; the subgenus Arzosciurus has 
two species and an additional subspecies in the United States, 
and three additional species and one subspecies in Mexico; Tamia- 
sciurus has three species and 15 additional subspecies. 
All the species of North-American Sciuri are sharply differ- 
entiated; the numerous subspecies represent for the most part 
well-marked geographical forms, which characterize more or less 
natural physiographic areas. In many cases the subspecies, 
in their extreme phases of development, are strongly differ- 
entiated, yet coalesce so completely at intermediate points 
as to be unsusceptible of sharp definition. They, however, 
represent stages in the evolution of species, and are facts that 
may be conveniently made note of by the brief formula of a 
trinomial name, 
