that Utah by its highly varied topography and climate possesses widely different types of habitats. The aforementioned plasticity of these animals and possibly the fact that both species are at the extreme limits of their ranges in Utah account for the numerous forms found within the state.

The genus may be characterized as follows: Highly specialized fossorial rodents, with heavy, thick bodies; all four legs of approximately equal length, but front legs more muscular for digging, and feet provided with long claws; external fur-lined cheek pouches; small eyes, short ears and tail; upper incisors long and projecting external to lips. Skull: Stout and flattened; zygomatic arches well developed and usually widely spreading; all teeth with permanent pulp cavities; incisors superficially smooth, but fine median groove present on anterior face of each upper incisor; dental formula, i. 1/1, c. 0/0, p. 1/1, m. 3/3; external auditory canal long; stapedial artery small and enclosed within an osseous canal.

Thomomys talpoides (Richardson)

Thomomys talpoides is a northern species that in Utah approaches the southern limits of its range. The animals of this species inhabit the mountains and high valleys. In the southward extension of their range, as in Utah, they are found at higher elevations which zonally represent lower elevations at more northern latitudes. The specific characters are: Sphenorbital fissure absent; incisive foramina anterior to infraorbital canal; anterior prism of P4 triangular; interparietal relatively large; lambdoidal suture concave posteriorly in region of interparietal, in Utah specimens.

Thomomys talpoides gracilis Durrant

Type.—Male adult, skin and skull; No. 44866, Museum of Vertebrate Zoölogy, University of California; Pine Canyon, 6,600 ft., 17 mi. NW Kelton, Box Elder County, Utah; July 12, 1930; collected by Annie M. Alexander; original number 676.

Range.—Mountainous regions of extreme northwestern Utah.

Diagnosis.—Size medium (see measurements). Color: Upper parts Buckthorn Brown grading over the sides and flanks to Light Buff on the underparts; chin white; nose and postauricular patches grayish black. Claws on front feet long and slender. Skull: Long and slender; rostrum long and narrow; zygomatic and mastoidal breadths slight; palatal pits deep; upper incisors narrow; basioccipital wide.

Comparisons.—Compared with topotypes of Thomomys talpoides fisheri, gracilis is of approximately the same size. Upper parts darker and underparts lighter; postauricular patches larger and darker; claws on front feet longer and slenderer. Skull: Generally longer and narrower; nasals and rostrum longer; basioccipital wider.

As compared with T. t. uinta, gracilis is of approximately the same size but differs as follows: Color: Lighter throughout; postauricular patches markedly smaller and lighter; inguinal and pectoral regions much lighter. One characteristic difference is in the ear. In uinta the external opening of the ear is much larger; the pinna of the ear is larger, more rounded at the tip, and lacks most of the pigmentation on the inner margin. Skull: Generally narrower and longer; nasals longer; zygomatic arches weaker and less angular; upper incisors narrower.

This form is easily distinguished from bridgeri by smaller size, and by the skull being longer, narrower and less angular.

From Thomomys talpoides oquirrhensis to the southeast, T. t. gracilis can be distinguished by: Total length and ear shorter. Color: Generally lighter, except the underparts which are about the same; postauricular patches larger and more deeply pigmented. Skull: Braincase less inflated; nasals truncated posteriorly as opposed to rounded; zygomatic and mastoidal breadths less; rostrum shorter but narrower; upper incisors narrower and shorter.

For comparisons with wasatchensis see comparisons under that form.

In general, this mountain form can be distinguished from all other talpoides in Utah by lighter color, narrow, slender, "graceful" skull whence the name gracilis is derived.

Remarks.—In Utah, gracilis is limited to the extreme northwestern corner of the state. This part of the state is in the Snake River drainage. The main part of the range of this race lies in south-central and southwestern Idaho and northeastern Nevada. The center of its range might be considered to be in the Jarbidge Mountains area of Nevada. The south slopes of these mountains are in the Humboldt River drainage, while the north slopes are in the Snake River drainage, and this subspecies occurs as far north as the Snake River and south and west almost to central Nevada. No specimens are available from the area in Utah between the Raft River Mountains inhabited by gracilis and the Wasatch Mountains in central Utah inhabited by wasatchensis. Judging from the nature of the terrain, the range of gracilis does not extend eastward much beyond the Raft River Mountains. The type locality for a gopher of a different species, Thomomys bottae aureiventris, is in the first valley east of these mountains. Furthermore, all valleys to the east and south, as far as known, are inhabited by gophers of the bottae group. Also, all mountain ranges in this area, as far east as the Wasatch Mountains are inhabited by members of the bottae group.

No specimens from Utah indicate intergradation between gracilis and wasatchensis, the form to the east, but specimens from farther north at Albion, Cassia County, Idaho, do show intergradation. Bailey (1915:116), Hall (1931:4), and Durrant (1939:6) have reported on these specimens which at the present time seem best referred to T. t. gracilis.

Thomomys talpoides wasatchensis new subspecies

Type.—Male, adult, skin and skull, No. 1604, Museum of Zoölogy, University of Utah; Midway, 5,500 ft., Wasatch County, Utah; September 1, 1936; collected by S. D. Durrant; original number 1049.

Range.—Wasatch Mountains and neighboring high valleys as far south as Spanish Fork Canyon, Utah County.