1912] Grinncll: The Bighorn of the Sierra Nevada 145 



this matter of pelage sierrae much more closely resembles cervina 

 than it does nelson i. 



Coloration. — In general tunc of coloration sierrae is dis 

 tinctly grayer, more ashy, than either nelsoni or cervina, of 

 comparable pelage. The Sierran form is perceptibly paler in 

 color than either, though the contrast is strongesl with cervina. 

 The white of rum]) area, belly, and hind sides of legs appears 

 to be purer in sierrae; but this is probably more apparent than 

 real, and is explanable because of the much longer hair, which, 

 especially when separated, shows a great extern 1 of clean surface. 

 The rum]) patch is so much heavier haired in sierra* than in 

 tielsoni, that the effect reminds one strongly of the antelope. 

 There is no appreciable difference between the two sheep, how- 

 ever, in relative extent of light and dark areas. 



Ears. — The smallness of the ears in the Sierran sheep as 

 contrasted with the relative largeness of these members in the 

 desert form, has several parallels among other mammals. The 

 conditions of sound transmission in the two sorts of environment 

 are probably to be called into account, so that as with quantity 

 of pelage, the differential feature in question is adaptive. The 

 differences in size of ears in the two forms are readily appre- 

 ciable upon comparison of the dry skins; the collectors' measure- 

 ments of {'height of ear." although probably not ascertained in 

 the different instances upon a uniform basis, give a fair index of 

 the amount of difference (see table of measurements). 



Tail. — The tail as shown from the external measurements is 

 distinctly shorter in sierrae than in nelsoni. In the latter it is 

 scantier haired, so that in effect it resembles the tail of Odocoi- 

 h its In niiinnis as compared with 0. columbianus, though the 



difference is not so extreme as between these two deer. 



General size. — The tables of measurements show sit rem , as 

 compared with nelsoni, to be distinctly larger, always considering 

 age; for it appears that sheep keep on growing throughout their 

 lifetime, though at a decreasing rate as age advances. Total 

 length, hind foot, and length of hoofs are all greater in sit rrat . 

 In these respects, the approach is again towards cervina. 



Horns. — A single feature of the horns is apparently of differ- 

 ential value, namely their form in cross-section at the base. In 



