414 U. Ss. P. R. R, EXP, AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
DIPODOMYS AGILIS, Gambel. 
Dipodomys agilis, GamBrn, Pr. A. N. Sc. Phila. IV, Aug. 1848, 77. (Los Angeles.) 
Leconts, Pr. A. N. Sc. Phila. VI, 1853, 224. 
Aup. & Bacu. N. Am. Quad. IIE, 1854, 339. 
Barrp, Pr. A. N. Sc. Phila. VI, 1855, 334. (San Diego.) 
Sp. Cu.—Above dusky, with but a slight tint of yellowish brown on the sides. Tail much longer than the body ; slender ; 
only a moderate crest of erect hairs towards the tip visible on both upper and under surfaces. The terminal fourth or fifth 
of the tail uniform dusky, and the dusky stripe on the lower surface extending to the end without interruption. 
In this species the body appears stouter than that of D. phillipii. The ears are large, with . 
the posterior half of the exterior surface sparsely coated with hairs ; the antitragus is as fully 
developed as in D. phillipii. The tail is slender, and much longer than the body, the hairs on 
the upper surface beginning to elongate about the middle, and maintaining an average length 
of about one-third of an inch to near the tip, where they become rather longer. At about the 
terminal fifth of the tail the hairs on the under surface elongate, and are quite symmetrical in 
length and angle of insertion with those above them. 
The prevailing colors are, on the back and sides, ashy brown, with the sides anterior to the 
groin tinged with yellowish brown, and a fine pencilling of the same on the shoulders and top 
of the head. The under parts generally, side of snout, spot above the orbit and behind the 
ear, with the feet and a stripe from the abdomen across the thighs to the root of the tail, 
white. The posterior face of the hind leg, from the hams to the toes, sooty brown. Tail dark 
brown, with a white stripe from the base to about the terminal fourth, which is quite uniformly 
dusky. None of these dark hairs have appreciably lighter bases. 
The hairs on the upper parts of the body are lead color, the tint becoming a little darker to the 
terminal pale tips, On the flanks the hairs with the yellowish brown tips are white at the base 
only along the line of junction, instead of having this character prevail for a considerable dis- 
tance up the sides. 
This species differs from D. phillipii in the stouter body, pedudles ears, shorter and less bushy 
tail, much darker tints on the body, and the uniform dark colors of the terminal fourth of the 
tail. The tail is longer and the colors darker than in D. ordii, which, besides, is without the 
uniform dark tip. 
A specimen from San Diego, (1062,) with the cinsishetes of the species described above, 
has the hairs at the end of the tail longer and fuller, and, when examined closely, they present 
a little whitish at the base, instead of being uniform plumbeous to the root. 
In the impossibility of settling the question without further materials, I have not thought it 
best, as yet, to combine all the long-tailed Dipodomys from the Pacific slope into one, but have 
not much doubt that such course will be authorized hereafter. The colors of body and tail vary 
very considerably at any rate; and to continue the construction of species on the same data as 
guided Dr. Leconte and myself two or three years ago, would now necessitate the establishment 
of half a dozen new ones, to accommodate the present large collection belonging to the Smith- 
sonian Institution. That we certainly have two very good and distinct species, the first extend- 
ing along the Rocky Mountains, from the Platte, to about latitude 26, in Coahuila ; the other 
from the Columbia river to San Diego, Fort Yuma, and, possibly, to Real del Monte, Mexico, 
