362 THE QUADRUPEDS OF ARIZONA. 
species are strictly terrestrial, and eminently gregarious, 
being noted for the large colonies which they form. Long 
as they have been known, and much as has been learned 
about them, there are many points of their social and in- 
dividual economy which remain very obscure. Such are 
those relating to their migrations, their supplies of food 
and water, their gestation, and their relations with the 
owls and rattlesnakes found among them. The common- 
est of our two species, C. Ludovicianus, is mainly confined 
to the great central plains. A second species occurs in 
Arizona; the short-tailed Prairie Dog (C. Gunnisonit 
Baird), named in 1855 from specimens brought from 
Coachetope Pass by Capt. Beckwith. It is distinguished 
from the other by its smaller size, somewhat different 
colors, and still shorter tail, which is not tipped with 
black. I was so fortunate as to secure a specimen of this 
rare animal, near the San Francisco Mountains, in July 
of 1864. A colony had settled in one of the little open . 
grassy glades which are scattered like oases through that 
wild and broken region. No owls or rattlesnakes were 
to be seen, though a species of horned toad (Phrynosoma 
Douglassii) was extremely abundant. Their cries, move- 
ments, and general manners were much like those of the 
common species. i 
Passing over the marmots proper (Arctomys), of which 
I have no knowledge as Arizonian animals, there only 
remains to be noticed one more member of the Sciurid@, 
—the Beaver (Castor Canadensis Kuhl). This animal 
differs in so many essential features, both external and 
anatomical, as well as in habits, from the family types» 
that naturalists doubt the propriety of retaining it in its 
‘present position. It is found abundantly on all the 
streams of the Territory. Judging from the accounts of 
