MAMMALS OF THE MEXICAN BOUNDARY. 



243 



rump blended with the coloring of the flank, instead of being sharply 

 defined. The muzzle is abruptly whitish in the northern animal and 

 unicolor with the rest of the head in the southwestern desert form. 

 Besides these differences, the median dark line which divides the white 

 of the rump into two parts is obsolete and noncontinuous in the south- 

 ern specimen, which also has more white on the inner side of the heel, 

 opposite the tibio-tarsal articulation. The summer female of 0. c. 

 gaillardi (No. 21392, U.S.N.M.) from the Gila Mountains, Arizona, 

 is much paler than one in corresponding pelage from Wyoming (No. 

 11891, U.S.N.M.) the former differing from the latter to about the 

 same extent that the winter skins just compared differed from each 

 other. The skull of an eld male from the Gila Mountains, Mexican 

 Boundary Line (No. 59907, U.S.N.M.), is broader across the fore- 

 head and has a stouter muzzle than an old male collected by 



Fig. 39.— Ovis canadensis. Skull of addlt male. Thkee Buttes, Montana. (Cat. No. 13962, 

 U.S.N.M.). a, LATEBAi VIEW; h, dorsal view. 



the Northern Boundary Survey in Montana (No. 13962, U.S.N.M). 

 The horns of the male of the Gaillard bighorn are curved in a closer 

 spiral than those of the northern typical form (fig. 39), and in 

 Ovis stonei," O. canadensis dalli, and 0. nivicolg, the tips of the 

 horns become more and more divergent. Two pairs of horns of 

 adult males were measured at Tina j as Altas, Yuma County, Arizona 

 (Nos. 59907 and 59908, U.S.N.M.), which were 720 and 820 mm., 

 respectively, in length, following the outer curves of the horns, and 

 365 and 360 mm. in circumference at base. The first horns of the 

 young male are quite different in form to those of the female. 



Geographical range. — Low desert ranges in the Austral Life Zone, 

 south of the Gila and east of the Colorado River, ranging south into 

 Sonora, Mexico, as far as Seriland, opposite Tiburon Island, in the 

 Gulf of California. 



<iOvis stonei Allen, Bull. Am. Mus. Nat. Hist, IX, Art. VII, April ]8, 1897, 

 pp. 111-114, pis. II, III. Type from the headwaters of the Stikine River, British- 

 Northwest Territory, near the Alaskan boundary, at an altitude of about 6,500 

 feet. 



