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1887] Description of a New Species of Dipodomys. 45 
the eye. A few passes and one or the other loses its balance 
and leaps away, followed a short distance by the other. I have 
been unable to detect any use of the teeth in such face-to-face 
encounters. Sometimes the larger D. deserti will happen near 
one of the others and slowly and slyly work closer, and suddenly 
pounce on the other, when I have.heard a squeak of pain as if 
the teeth had been used. The bite cannot be severe, for the mouth 
is not capable of opening widely, and the upper incisors slope 
inward so much that they can get but a shallow hold. I have not 
handled the D. phillipsi much, but they have never bitten me. I 
handle the D. deserti often; one has never bitten me, the other 
but once, when I attempted to hold it against its wishes. It bit the 
inside of my forefinger where the skin was thick, and though the 
teeth met, but a drop or two of blood flowed. The punctures 
made by the upper and under incisors were but five-thirty-seconds 
of an inch apart, and I believe it was about as hard a bite as 
the beast was able to inflict on so comparatively flat a surface. 
Of course they are capable of cutting a twig or similar hard sub- 
stance of small size. They have not so far attempted to bite the 
tail of another, which is the favorite mode of attack of their rela- 
tives, the tuft-tailed pocket-mice (Perognathus penicillatus). Loco- 
motion is similar with both species, but D. phillipsi is more agile, 
leaping farther and quicker. This species can reach to about 
eighteen inches from the floor in trying to escape from the room, 
the leap taking place from near the foot of the wall. I think the 
usual horizontal leap when running rapidly is three feet or more, 
which is considerably more than that of D. deserti. The gait 
might be termed a hop, the work being mostly done with the 
hinder limbs. When moving about slowly, the first movement 
seems to be a tap on the ground with the fore feet to raise the 
fore part of the body to a leaping position, when the powerful 
hinder limbs give a spring resulting in a leap of a few inches. 
When they are running rapidly one cannot see just how it is 
done, but I often thought that the fore limbs take little or no 
part in the action, which seems to be aided by the long tail, both 
in guiding and balancing. It certainly looks as if the animal 
would be in danger of running its nose in the ground and “ end- 
ing over” if it depended on its very short fore legs to raise its 
body into leaping position after each quick leap, for D. phillipsi 
at least can get over the ground at a pace that would put a cat 
