820 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
is a heterogeneous group, embracing quite diverse species, some of which 
strongly approach Sciurus, while others foreshadow Cynomys, and others 
still grade by almost insensible stages into Tamzas. The group was first dis- 
membered* by Brandt in 1844, who divided it into two “subgenera”, namely, 
Colobotis (also written later in the same paper “ Otocolobus”) and Otospermo- 
philus. To the first he referred all the Old World species known to him, and 
also three of the North American species; the latter is exclusively American. 
These two groups are based on slight peculiarities of dentition (particularly 
in respect to the size and form of the first upper premolar), the size of the 
ear, and the length of the tail. The Old World species of Colobotis are all 
short-tailed, with small or rudimentary ears, the tail with the hairs exceeding 
a length of two inches in only one species (S. eversmanni), being generally 
considerably less than one-fourth of the length of the head and body. Only 
one (S. richardsonz) of the three American species referred by Brandt to this 
group really belongs here, the others (9. “‘hoodi” = tridecemlineatus, and S. 
Jranklini) having few characters in common with the others. O¢ospermophi- 
Jus is a much more natural division, but was made to include S. mezicanus, 
which, as will be shown later, belongs to a wholly different division. The 
other species referred to Otospermophilus were S. granmurus (with its varie- 
ties and synonyms) and S. /ateralis; the affinities of the last named are 
divided between this group and Tamas, with a preponderance toward the 
latter. Brandt divided the Old World representatives of Colobotis into three 
sections (“A”, “B”, and “C”), based wholly on the seasonal and valueless 
character of the pilosity of the soles, which he appears to have supposed to 
be a constant character in adults. His section ‘‘B” (consisting of S. evers- 
manni and S. parryz) he says resembles Otospermophilus in the length and 
structure of the tail. This is also true of other characters; it hence forms 
a natural and well-marked subdivision of his subgenus Colobotis. 
In 1855, Brandt’s divisions and subdivisions were adopted by Giebel. 
Baird, in 1857, while pointing out the worthlessness of any distinctions based 
on the pilosity of the soles, thought Brandt’s subgenus Osospermophilus euti- 
tled to permanent recognition, and adopted it with merely the removal there- 
from of S. mexicanus to Colobotis, under which latter group Professor Baird 
* Lichtenstein, however, about 1830, proposed the name Citillus for certain species, but without 
giving for the group any tangible diagnosis. The first species described under this name was S. mezi- 
canus, but be also described two Old World species (C. fulvus and C. mugosaricus) that differ widely from 
S. mexicanus, belonging in fact to an entirely different section of the genus. Brandt makes, and quite 
properly, as it seems to me, Citillus merely a synonym of Spermophilus. 
