394 THE QUADRUPEDS OF ARIZONA. 
tially subterranean and nocturnal, often come abroad in 
the daytime. They are known in the vernacular as 
“Kangaroo” or “Jumping” Rats and Mice, and are en- 
tirely confined to Transmississippian regions. The larg- 
est species is about as big as a third-grown rat, while the 
smallest is among the most diminutive of all our animals, 
unless some of the shrews are still less in size. These 
animals have well-formed bodies, very large and muscu- 
lar thighs, small hands, large rounded ears, full protu- 
berant eyes, and very long tails, often tufted at the end. 
Their fur is peculiarly soft and lustrous. 
The two genera of the Geomyine, though very similar 
to each other, are distinguished, among other features, 
by the absence in Thomomys of the deep central longitu- 
dinal grooves in the upper incisors which exist in Geo- 
mys. The latter is hardly known west of the Rocky 
Mountains, nor the former to the eastward of them. 
Though two other species may occur in Arizona ( Thom- 
omys bulbivorus from California, and T. umbrinus from 
Sonora), only one, the Red Sand-rat (T. fulvus) is at all 
common. It was discovered by Dr. Woodhouse in the 
vicinity of the San Francisco Mountains, where it is ex- 
ceedingly abundant. It lives mainly in light sandy or 
loamy soil, such as may be readily excavated. “The soft 
soil of grassy hill-sides, or sloping meadows, especially in 
the vicinity of oaks, or clumps of nut-bearing trees, are 
favorite resorts, as it finds there an abundance of acorns, 
seeds, and grasses, upon which it feeds. The succulent 
stems and roots of many herbs also furnish it with food. 
Wherever it takes up its abode, little piles of fresh moist 
earth may be seen in every direction, sometimes scores 
within a radius of as many yards. These are especially 
noticeable in the morning, for the animal is strictly 
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