33<) BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



CITELLUS TERETICAUDUS (Baird). 

 YTJMA GROUND SQUIRREL. 



Spermophilus tereticaudus Baird, .Mam. N. Am., 1857, p. 315 (original descrip- 

 tion); Rep. U.S. Mex. Bound. Surv., II, Ft. 2, Mam., L859, p. 38, pi. vn, 

 6g. 2 (head and feet); pi. xxn, fig. 4 iskull). — Allen, Proc. Bost. Soc. 

 Nat. Hist., XVI, 1S74, p. 291.— True, Proc. U. S. Nat, Mus., VII, 1885, 

 p. 594.— Miller and Keiin, Proc. Bost. Soc. Nat, Hist., XXX. No. 1, Dec. 

 1'7, 1901 (Syst. Results Study N. Am. Mam. to close of 1900). 



Spermophilus I Tctidomys) tereticaudus, Meakns, Bull. Am. Mus. Nat. Hist., I, No. 7, 

 .Tidy, 1886, pp. U>7-L'07 (Arizona). 



[Spermophilus (XerospermophUus)] tereticaudus, Elliot, Field Col. Mus., Zool. 

 Ser., II, 1901, p. its (Synop. Mam. N. Am.). 



[Citellus | Xerospermophilus)~\ tereticaudus, Elliot, Field Col. Mus., Zool. Ser., IV, 

 1904, p. 144 (Mam. Mid. Am. |. 



Type-locality. — Old Fort Yuma, Sun Diego County, California (oil 

 the right hunk of the Colorado River, opposite the mouth of the Gila 

 River and the present town of Yuma, Arizona). (Type, skin and 

 skull. No. |H|, U. 8. National Museum). 



Geographical range. — Lower Sonoran Zone of the Western Desert 

 Tract; from Fort Lowell and La Osa on the east to the Coast Range 

 Mountains on the west. 



Description. -Size small. Length, 250 mm. ; tail vertebra}, 97; hind 

 foot, 36; ear rim, 3; head, 42. Skull 38 by 24. Form slender; head 

 short: ear reduced to a mere rim: tail cylindrical, with hairs appressed. 

 There are ."> pairs of mammary teats (in one ease, six pairs). Iris dark 

 brown. Claws purplish black, tipped with horn color. Colorin win- 

 ter pinkish buff above, withsome hoariness, white below: tailconcolor 

 with the body above, yellower below, and obscurely annulated; feet 

 white; pelage tine, with copious under fur which is plumbeous at base 

 and white at tip. In summer vinaceous- buff above, mixed with a few 

 black and a few white pointed hairs; pelage short and coarse, without 

 under fur, and not concealing the skin below. In coloration, the 

 young closely resemble their parents. 



Cranial ami a\ ntal characters. -Skull (fio-. 55) short, broad, broadly 

 arched interorbitallv; rostrum abbreviated; audita] bullae large, deep, 

 and very evidently lobed by deep vascular channels; interpterygoid 

 fossa narrow; malar arches very strong and much everted. Dentition 

 strong; lateral rows of teeth approximated posteriorly, with the 

 molars set very obliquely. 



Remarks. — Molting begins in March. Nursing females taken on 

 the Colorado Desert during the last week of April and first week in 

 May were all in summer pelage— except the tail, the last part to 

 change. Specimens from (he Tide and Yuma deserts, to the eastward 

 of the Colorado River, are more reddish than those taken at the same 



