Upon separating the hairs of the middle region of the back about a third of the distance between the ears 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 vertebrae, 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: 

     [Transcriber note:  Next line was corrected per erratum.  The
     original text was of the following paragraph (Averages for 17
     adult females:  Total length, 326.4 millimeters).]

Average measurements of 30 adult specimens of both sexes:  Total length, 326.2 millimeters (349-310); tail vertebrae, 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 vertebrae, 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 vertebrae, 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.