670 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
of note that the smallest species (Sciwrus hudsonius) is the most northern, 
and that the next smallest (Sctuzus @stuans) is the most southern, both 
occurring on the extreme boundaries of the habitat of the group. These 
again, in respect to the development oi the tail, are the least Sciurine; the 
long, full, bushy, distichous tail, so characteristic a feature of the Sciwri as 
distinguishing them from their allies, being in these two species very much 
shorter and narrower than in any of the others. In passing southward, we 
meet, next after S. hudsonius, with S. carolinensis, a species again below the 
average in size, with the tail only moderately developed, although there are 
some Mexican and Central American species equally small. The largest 
species, as well as the greatest number, and those with the largest tails, are 
Mexican; Western and Southern Mexico being apparently the centre of devel- 
opment, or metropolis of the group, as respects the two Americas. None are 
thus far known from any of the intertropical islands. 
As already observed, the American Sciwri form a group so homogeneous 
as not to be readily subdivisible. Taking, however, the relative length of the 
tail, and the number and character of the upper premolars, as a basis, with such 
other features as are most readily available, the species and subspecies may 
be conveniently (and somewhat naturally) grouped as follows :— 
SYNOPSIS OF THE SPECIES AND SUBSPECIES OF AMERICAN SCIURI. 
I. Tail very short and narrow, the caudal vertebra alone about two-thirds as long as the head and body ; 
tail to end of hairs abont one-seventh shorter than the head and body; premolars }, the 
first very small and often deciduous; a narrow, black, lateral line; size small. One 
species with four subspecies : 
1, Above grayish, mixed with yellowish or reddish, annulated with dusky, often with a strong 
wash of ferruginous along the middle of the back; below generally white, sometimes 
narrowly annulated with black; in one subspecies fulvous below. Hab.—Northern half 
of North) Americas. 2-2-2. c.-seee=e esis Sach boteelesiecltennieeineaeL eared S. HUDSONIUS. 
a, Above yellowish-gray, varied with black, with generally the middle of the back strongly 
washed with ferruginous; upper surface of the tail with the hairs rusty at the base and 
reddish-tipped, with a broad subterminal bar of black. Hab.—Northern North America 
east of the Rocky Mountains and northwestward to Alaska ........--.-var. hudsonius, 
b. Above varied with black and yellowish-rusty ; upper surface of the tail with the bairs gray 
at the base and gray-tipped, with a broad subterminal bar of black. Hab.—Central portion 
of the Rocky Mountains, and thence westward to the Sierra Nevadas....var. fremonti. 
c. Above dusky, strongly varied with reddish; upper surface of the tail with the hairs dark 
reddish-brown at the base, tipped with reddish, and with a very broad subterminal 
bar of black, sometimes occupying the whole of the terminal third. Hab.—Rocky 
Mountains between latitude 438° and 52°, and thence westward to the Cascade 
Ranges. 525.0230. s 0025 52 eee ee eee ee eee var, richardsoni. 
d. Above as in the preceding (var. richardsoni); tail with less black; beneath more or Jess 
strongly tinged with fulvous or rufous. Hab.—Pacifie-coast region from Northern Cali- 
forniaito Sitka. 22-2 (sock ee ee ee ee ee: var. douglasst. 
