RODENTJA-MURIJVAE-HESPEROMYS EREMICUS. 
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especially between tbe arms, while the chin and throat have a more grayish aspect. The tail 
is brown, only a little darker along the median line. 
This animal is more than twice the size of the naked heeled species from Fort Yuma, and is 
much darker throughout, though in many respects quite similar. 
This species inhabits nests of Neotoma fuscipes, in Santa Clara valley, composed of sticks, 
twigs, and leaves, and forming a large mass. On setting fire to these nests, both species rush 
out together. The precise character of the domestic relations of the two animals is not known. 
At first the Hesperomys was taken by Dr. Cooper to be the young of the Neotoma , but an 
examination clearly revealed the generic peculiarities of each. The feet of the mouse are 
longer in proportion, especially the toes, and more naked ; the tubercles smaller, and the ears 
larger and differently constituted. 
There is little doubt that this is the species briefly indicated by Dr. Gambel in 1848, as no 
other on the west coast presents anything like the size of body, tail, and ears. It is somewhat 
to be regretted that the very appropriate name of parasiticus , selected by Dr. Cooper to express 
the habits of the animal, as mentioned above, could not be retained. Dr. Gambel’s specimen 
was taken at Monterey, which thus extends somewhat the known range of the species. 
List of specimens. 
HESPEROMYS EREMICUS, Baird. 
Desert Mouse. 
Sp. Ch.—S ize of II leucopus, or less ; ears, very large ; tail, considerably longer than the body ; fingers and toes, short; 
color above, grayish yellowish ; a pale fulvous band on cheek and sides; tail, scarcely lighter beneath ; feet, and under parts, 
snowy white. Soles entirely naked. 
This species is at once characterized among the smaller American species by having the soles 
entirely naked from the heel, and covered with a pavement of granular scales. In other respects 
the feet resemble those of Hesperomys leucopus quite closely, except that the middle toes of the 
hind feet are shorter, the fifth claw reaching to the base of the fourth, instead of falling a little 
short of it. The posterior tubercle is smaller and rounder than in this species, and its anterior 
edge is posterior to a point midway between the heels and balls of the toes. The next anterior 
tubercle (or the outer edge) is smaller, and much less than in H. leucopus. The fore feet exhibit 
the same brevity of the fingers. The feet, generally, are more like Neotoma than Hesperomys. 
The ears are very large, longer than broad, not quite as much rounded at the tip as in H. 
