1915.] 



THOMOMYS TALPOIDES GROUP. 



109 



Characters. — Size very small; color pale yellowish gray; ears small; 

 skull light and smooth, with very large and globose bullae and incurved 

 upper incisors; mammae in 6 pairs, inguinal 2-2, abdominal 2-2, pec- 

 toral 2-2. 



Color. — Summer pelage: Upperparts pale dull olive-buff or buffy 

 gray; ear with only a trace of dusky patch; nose yellowish; under- 

 parts pale buff or soiled whitish, occasionally with white chin; feet 

 and tail very hairy, pale buffy or whitish. Young, more ashy gray. 

 Winter pelage unknown. The summer pelage is decidedly paler than 

 the corresponding pelage of ocius, hence the winter pelage is probably 

 lighter colored than in any other northern species of the genus. 



Slcull. — Of much the same general form as in ocius, but conspicu- 

 ously smaller and smoother with smaller, more oval interparietal; 

 nasals minutely notched at posterior tip and ending approximately 

 even with premaxillse ; audital bullae very large and globose, sometimes 

 actually meeting over narrow shaft of basioccipital. While the ex- 

 ternal ear is very small, the auditory meatus and audital bullae are 

 unusually developed, the bullae being relatively the largest of any 

 species of the genus. 



Measurements. — Type ( c? ad.): Total length, 179; tail vertebrae, 

 47; hind foot, 23. Average of 10 male topotypes: 179, 50, 22.5. 

 Average of 9 female topotypes: 166, 49, 22.4. Ear, from base, meas- 

 ured in flesh, 4.5. Slcull (of type): Basal length, 29.5; nasals, 11.5; 

 zygomatic breadth, 18; mastoid breadth, 16; interorbital breadth, 

 4.7; alveolar length of upper molar series, 5.5. 



Remarlcs. — The type locality is at the extreme upper edge of the 

 Upper Sonoran Zone and the upper limit of the range of the species. 

 This gopher is a small, pale, desert species of the Snake River Plains. 

 There is no indication of its intergradation with any of the surround- 

 ing forms, and its nearest relative is ocius of the upper Green River 

 Basin in Wyoming. The boundary of its range rernams to be worked 

 out, and winter or early spring specimens are greatly needed to show 

 the winter pelage. 



Specimens examined. — Total number, 42, as follows: 

 Idaho: Big Butte, 2; Big Lost River (near Sink), 3; Birch Creek (10 miles south 

 of Nicholia, 6,400 feet altitude), 21; Blackfoot, 11; Dubois, 1; Idaho Falls, 

 1; Sink of Birch Creek (5,100 feet), 3. 



THOMOMYS PYGMiEUS Merriam. 

 Pygmy Pocket Gopher. 

 (PI. vn, fig. n.) 



Thomomys pygmxus Merriam, Proc. Biol. Soc. Washington, XIV, 115, July 19, 1901. 



Type. — Collected at Montpelier Creek (exact locality about 10 miles 

 northeast of Montpelier, at 6,600 feet altitude, in open sagebrush of 



