83<J BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



CITELLUS TERETICAUDUS (Baird). 

 YUMA GROUND-SaUIRREL. 



S/)/'nnuj)ltl/iis tert'tlcaudii.s Baikd, Mam. N. Am., 1857, p. 315 (original descrip- 

 tion); Rep. U. S. Mex. Bound. Siirv., II, Pt. 2, Mam., 1859, p. 38, pi. vii, 

 tig. 2 (head and feet); \)\. xxii, fig. 4 (skull). — Allen, Proc. Bost. Soc. 

 Nat. Hist., XVI, 1874, p. 291.— Trie, Proc. U. S. Nat. Mus., VII, 1885, 

 p. 594.— MiLLEK and Rehn, Proc. Bost. Soc. Nat. Hist., XXX, No. 1, Dec. 

 27, 1901 (Syst. Results Study N. Am. Mam. to close of 1900). 



Spermophilus {Icti(1onjtyi<)ipreticuudns, Mearns, Bull. Am. Mus. Nat. Hist., I, No. 7, 

 July, 1886, pp. lW-207 (Arizona). 



[Spermophilns {Xerospennophilus)] lereficatiduti, Kluot, Field Ciil. Mus., Zool. 

 Ser., II, 1901, p. 98 (Synop. ]Mam. N. Am.). 



[(JItellus {Xerosperniopliiliis)^ tereticandux, Elliot, Field Col. Mus., Zool. Ser., IV, 

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



Tt/pe-Iocaliff/.- 0]d Fort Yuma, San Diego County, California (on 

 the right l)ank of the Colorado Kiver, oppo-site the mouth of the Gila 

 River and the ])re.sent town of Yuma, Arizona). (Type, skin and 

 skull. No. ^f^l, U. S. National Museum). 



Gcixjiuipliical range. — Lower Sonoi-an Zone of th<' Western Desert 

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

 Mountains on the west. 



I)excrij>fl()n. — Size small. Length, 250 mm. ; tail vertebra*, 97; hind 

 foot, HH; ear rim, 3; head, 42. Skull 88 by 24. Form slender; head 

 short; ear rediu-ed to a mere rim; tail cylindrical, with hairs appressed. 

 There are 5 pairs of mammary teats (in one case, six pairs). Iris dark 

 l)i-()wn. Claws purplish black, tipped with horn color. Color in win- 

 ter puikish butt' above, with some hoariness, white below; tailconcolor 

 with tlie body above, yellower V)elow, and obscurely annulated; feet 

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

 and white at tip. In summer vmaceous-butt' above, mixed with a few 

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

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

 young closely resemble their parents. 



Cranud and dirntal cJiaracters. — Skull (tig. 55) short, broad, broadly 

 arched interorbitally; rostrum abbreviated; audital bulla? 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 the Tule and Y^'uma deserts, to the eastward 

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



