and the rump, one uncovers a prominent gland, elliptical in outline, with long axis longitudinal and about 9 millimeters in length. The gland presents a roughened and granular appearance, and fewer hairs grow upon it than elsewhere on the back. The hairs in the vicinity are frequently matted, as if with a secretion. In worn stage of pelage the gland may be visible from above without separating the hairs. Bailey has suggested that this functions as an oil gland for dressing the fur, and our observations bear out this view. Kangaroo rats kept in captivity without earth or sand soon come to have a bedraggled appearance, as if the pelage were moist. When supplied with fine, dusty sand, they soon recover their normal sleek appearance. Apparently the former condition is due to an excess of oil, the latter to the absorption of the excess in a dust bath. The oil is doubtless an important adjunct to the preservation of the skin and hair amid the dusty surroundings in which the animal lives.

MEASUREMENTS AND WEIGHTS.

External measurements include: Total length, from tip of nose to tip of tail without hairs, measured before skinning; tail vertebræ, length of tail from point in angle when tail is bent at right angles to body to tip of tail without hairs; and hind foot, from heel to tip of longest claw.

The following are measurements of a series from the U. S. Range Reserve:

Average measurements of 30 adult specimens of both sexes: Total length, 326.2 millimeters (349-310); tail vertebræ, 188.4 (208-180); hind foot, 49.5 (51-47); the average weight of 29 adult specimens of both sexes was 114.5 grams (131.9-98.0).

Averages for 17 adult females: Total length, 326.4 millimeters (349-310); tail vertebræ, 188.8 (208-179); weight (16 individuals), 113.7 (131.9-98.0); excluding pregnant females, 13 individuals averaged 112.9 grams (131.9-98.0).

Averages for 13 adult males: Total length, 326 millimeters (345-311); tail vertebræ, 187.8 (202-168); weight, 116.8 grams (129-100).

There appears to be no significant difference in the measurements and weights of males and females, with the possible exception of the comparison of adult males and adult nonpregnant females.

OCCURRENCE.

GENERAL DISTRIBUTION.

Dipodomys spectabilis spectabilis is found in southeastern Arizona, in northwestern, central, and southern New Mexico, in extreme western Texas, in northern Sonora, and in northern and central Chihuahua (Fig. 1). A subspecies, D. s. cratodon Merriam, has been described from Chicalote, Aguas Calientes, Mexico, the geographic range of which lies in central Mexico in portions of the States of Zacatecas, San Luis Potosi, and Aguas Calientes.

HABITAT.

In the Tucson region spectabilis is typically a resident of the Lower Sonoran Zone. This is perhaps the principal zone inhabited over its entire range, but the animal is often found in the Upper Sonoran also, and in the Gallina Mountains of New Mexico Hollister found it invading the yellow pine Transition where the soil was dry and sandy and the pine woods of open character. The same observer found it common in grassy and weed-grown parks among the large junipers, pinyons, and scattering yellow pines of the Bear Spring Mountains, N. Mex. Bailey calls attention to the fact that the animal apparently does not inhabit the lower half of the Lower Sonoran Zone, as it extends neither into the Rio Grande Valley of Texas nor the Gila Valley of Arizona. In extreme western Texas it is common at the upper edge of the arid Lower Sonoran Zone, and in this region does not enter the Upper Sonoran to any extent.

In July, 1914, Goldman found this kangaroo rat common on the plain at 4,600 feet altitude, near Bonita, Graham County, Ariz., and noted a few as high as 5,000 feet altitude on the warm southwestern slopes of the Graham Mountains, near Fort Grant. Apparently spectabilis reaches its upper altitude limit in the Burro Mountains, N. Mex., where Bailey has found it sparingly on warm slopes up to 5,700 feet, and at the western base of the Sandia Mountains, east of Albuquerque, N. Mex., where dens occur at approximately 6,000 feet.

About Tucson it is undoubtedly more common in the somewhat higher portions of the Lower Sonoran Zone, above the Covillea association, than elsewhere (Pl. IV, Figs. 1 and 2). A few scattered dens are to be seen in the Covillea belt, but as one rises to altitudes of 3,500 to 4,000 feet, and the Covillea is replaced by the cat's-claws (Acacia sp. and Mimosa sp.) and scattered mesquite (Prosopis), with the Opuntia becoming less abundant, kangaroo rat mounds come more and more in evidence. Here is to be found the principal grass growth supporting the grazing industry, and the presence of a more luxuriant grass flora is probably an important factor in the greater abundance of kangaroo rats, both spectabilis and merriami. In this generally preferred environment the desert hackberry (Celtis pallida) is one of the most conspicuous shrubs; clumps of this species are commonly accompanied by kangaroo rat mounds.

In order to ascertain whether the banner-tailed kangaroo rat has any marked preference for building its mounds under Celtis or some other particular plant, all the observable mounds were counted in a strip about 20 rods wide and approximately 4 miles long, an area of approximately 160 acres, particular note being taken of the kind of shrub under which each mound was located. Of 300 mounds in this area, 96 were under Prosopis, 95 under Acacia, 65 under Celtis, 11 under Lycium, 31 in the open, 1 about a "cholla" cactus (Opuntia spinosior), and 1 about a prickly pear (Opuntia sp.). There is apparently no strongly marked preference for any single species of plant. While both desert hackberry and the cat's-claws afford a better protection than mesquite—since cattle more often seek shade under the latter, and in so doing frequently trample the mounds severely—it appears that the general protection of a tree or shrub of some sort is sought by kangaroo rats, rather than the specific protection of the thickest or thorniest species.

The following records indicate particular habitat preferences of spectabilis as noted at different points in its range: