398 THE QUADRUPEDS OF ARIZONA. 
unfrequented portions of the Territory, though the usual 
number of them exist at our various footholds on the 
Colorado River. In the interior, the indigenous species 
hold full sway, or at least did so two or three years — 
ago,—the time of which I write,—though since then 
the Brown Rat (Mus.decumanus), and the House Mouse 
(Mus musculus) may have migrated all over the Terri- 
tory, or been transported wherever the white man has 
settled. 
The genus Hesperomys is, perhaps, the best represented 
of the Sigmodontes. At least one species (H. eremicus 
Baird) is very abundant, both along the Colorado valley 
and the interior of the Territory. I found it very nume- 
rous at Fort Whipple, where it in a great measure seemed 
to abandon its primitive habits, and take up its residence _ 
as a veritable house mouse in buildings, particularly our 
granaries and store-rooms. It was sufficiently numerous 
to become quite an annoyance, sharing the plunder and 
comfortable home with the Kangaroo Rats. It ordinarily 
lives in bushes, brush-heaps, scrubby trees, etc., where 
it builds a somewhat bulky nest, of a globular shape, of 
grasses compactly matted together, and warmly lined. 
Another species (H. Sonoriensis) which I have never per- 
sonally met with, occurs in the southern portions of the 
Territory. Mr. Clarke says that it seems to live, as cit- 
cumstances may determine, either in the ground or in 
hollow trees. The species (or perhaps only variety of 
H, leucopus) called H. Texensis by Dr. Woodhouse, may 
also occur in South-eastern Arizona. 
The genus Reithrodon (of which the little Harvest- 
mouse of the Southern States (Reithrodon humilis) is a — 
_ typical species) is very similar to Hesperomys, but the 
upper incisors are longitudinally grooved instead of being 
