RODENTIA—DIPODINAE—JACULUS HUDSONIUS. 431 
The ears are moderately large, and differ from those of Hesperomys in the existence of a well 
developed and thickened antitragus in the form of a circular thickened pad, naked on the inside, 
and capable of being applied against the meatus, so as to close it entirely as in the shrews. The 
tragus itself, also, is unusually prominent, and doubtless aids in closing the ear. The eyes are 
small, situated nearly midway between the nose and the ear. 
The feet and hands are all unusually large, the former especially so. The thumb is very rudi- 
mentary, covered by a broad truncated nail. The third and fourth fingers are longest. The 
hind feet are very long, exceeding the skull and the tibia. The first toe is small, and placed 
so far back that its claw only reaches the end of the metatarsal ; the fifth claw reaches the 
penultimate articulation of the fourth toe. The second, third, and fourth toes are much the 
longest, the third slightly longest of all. The middle toes are as long as the hand, and half the 
distance from heel to end of metatarsals. The sole is entirely naked fromthe heel. There is a 
tubercle about midway between the heel and the end of the toes; one at the base of the first 
and the fifth, and another at the junction of the second and third, and third and fourth toes, 
making five in all. The four at the bases of the toes are small, conical, and not at all conspicu- 
ous. The sole to the first mentioned tubercle is quite smooth; beyond this it is covered by a 
pavement of granules, except on the toes, which are transversely scutellate. There is a decided 
palmation at the bases of the toes, especially between the third and fourth, where it extends to 
the penultimate articulation. 
The tail is very long, almost twice the body and head. It is éeltedrtat: or tapering gently 
to an attenuated tip ; it is covered with verticellate scales, with short hairs of equal length 
springing between the whorls and not concealing them at all. There is a very slight pencil at 
the end. (2593.) 
This species varies somewhat in its tints, although the pattern remains much the same. A 
well defined area—bounded by lines commencing at the nostrils and proceeding backwards 
immediately under the eye and meatus, and along the sides of the back, slightly divergent to the 
rump, and then converging to the root of the tail—is of a light yellowish brown, much darkened 
by fine linings of black. Below this, on each side, and in strong contrast to it; is a broad 
stripe of nearly pure yellowish rusty, which involves the entire cheeks from the angle of the 
mouth, the whole exterior of the limbs to the wrist and heel, as well as the buttocks. On the 
middle of the side this is nearly as wide as the dorsal stripe at the same place. The under 
parts are pure white to the roots of the hairs; the feet hoary gray. The tail is whitish beneath ; 
dusky above. 
The colors vary in the lighter or darker tints of the sides, which sometimes have even an 
orange cast. Sometimes there is a development of black tips to hairs on the side, obscuring the 
colors, although the contrast to the back is always strongly marked. 
In the examination of a large number of specimens, I find a great difference in size as well as 
in the proportions of the tail. Asa general rule, however, specimens from the Rocky Moun- 
tains and the Pacific coast are much larger than eastern ones. I can at present distinguish no 
other differences of importance; and although, if they are the same, it would form rather an’ 
exception to the usual law of geographical distribution of our small rodents, I am not willing 
to establish a species on this ground alone. 
I hardly think that the Meriones acadicus of Professor Dawson is distinct as a species, as I 
find among the specimens in the Smithsonian collection every gradation between types of his 
two supposed species, kindly lent by him for examination. The larger feet of the smaller 
