All the specimens of this species from the desert slope of the San Gabriel Range are referred to the subspecies _perplexus_. They were taken in brushy habitats between the elevations of 4500 and 7400 feet. Throughout much of this area _perplexus_ was found only in certain restricted areas more or less surrounded by inhospitable ground. For example, at 7400 feet on Blue Ridge, they were found occasionally in the strips of sagebrush and lilac brush which locally capped this ridge. Often these patches of chaparral on Blue Ridge were surrounded by areas unsuitable for kangaroo rats: on the Pacific slope, talus, oaks, and yellow pines prevailed; on the ridge scattered yellow pine groves were present; and on the steep desert slope there were yellow pines and white firs. In Swarthout Valley _perplexus_ was found in flats that supported basin sagebrush and _Haploppus_, while the coniferous forests to the south, and pinyon-covered slopes to the north were uninhabited. On flats supporting antelope brush and juniper, _perplexus_ was often common, but it did not penetrate the chaparral of adjacent slopes grown to scrub oak and mountain-mahogany. In general then, _perplexus_ was found in fairly open brushy flats or slopes, even where these were surrounded by unsuitable habitats. Specimens of _D. agilis_ from the desert slope two miles east of Valyermo are referrable to the subspecies _perplexus_. A series taken in Cajon Wash at Devore, on the Pacific slope, is intermediate between _agilis_, of the coastal slope of the San Gabriels, and _perplexus_ of the desert slope, but approaches more nearly the later subspecies. Thus, different subspecies of _D. agilis_ occur on opposite slopes of the San Gabriel Mountains, with intergradation taking place in the Cajon Pass area and probably also at the west end of the Mountains. Both scrub oak acorns and juniper berries were found in the cheek pouches of this subspecies, and one immature individual taken in Swarthout Valley had its cheek pouches stuffed with approximately 550 seeds of brome grass. On November 13, 1951, at 7500 feet on Blue Ridge, a small juvenile was taken; it must have been born not earlier than September. _Specimens examined._--Total, 17, distributed as follows: Los Angeles County: 2 mi. E Valyermo, 4600 ft., 3; 5 mi. E Valyermo, 1; 1 mi. E Big Pines, 6600 ft., 6; 1 mi. S and 2 mi. W Big Pines, 7400 ft., 2. San Bernardino County: Cajon Wash, 1/2 mi. SW Devore, 2200 ft., 5. Family CRICETIDAE =Reithrodontomys megalotis longicaudus= (Baird) Western Harvest Mouse