10 



from a herd of ten old bulls that had strayed far to the eastward of 

 the main herds. It is but two or three years, however, since they 

 ranged one hundred to two hundred miles east of the Yellowstone in 

 the latitude of Fort Rice. 



11. Ovis montana Cuv. Bighorn. Rocky Mountain Sheep. 

 Not common. First met with in the Bad La ml.-, near the head of 



Glendive Creek, and seen occasionally in the Bad Lands that border 

 the Yellowstone. Not more than six or eight were- secured by the 

 hunters and scouts altogether, though their fresh tracks were quite 

 abundant at a few localities. 



ANTILOCAPRID^l. 



12. Antiloeapra americana Ord. Pronghorn. " Antelope." 

 Generally distributed, and more or less common. Most frequent, 



however, between the Missouri and Little Missouri Rivers. 



During the summer of 1873 a fatal epidemic raged among the 

 prong-horns over nearly the whole area between the Yellowstone and 

 Missouri Rivers, destroying apparently three-fourths to nine-tenths of 

 them. The greatest fatality seems to have occurred in July, judging 

 from the size of the fawns found dead, and hence not long after we 

 crossed this portion of the country. From the head of Heart River 

 to the Missouri we found their carcasses, on our return, thickly scat- 

 tered along our line of march, including those of both sexes and all 

 ages, fawns being often found lying within a few yards of their dams. 

 On our way out antelopes were almost constantly in sight, but on our 

 return they were only rarely met with, ten dead ones being seen to 

 each living one. The epidemic seems not to have extended beyond 

 the Yellowstone, where they seemed more numerous on our return 

 than on our way out, and where no dead ones were observed. 



The previous year they are reported to have ranged over this sec- 

 tion of the country, in autumn, in very large numbers, bands of two 

 or three hundred being sometimes met with by the Yellowstone 

 Expedition of 1872, on its return eastward. Four were captured by 

 the men as the frightened animals attempted to run through the train. 



Epidemics similar to that affecting the prong-horns, are well known 

 to occasionally affect deer, rabbits and field mice. A few years since 

 (about 1869) the Jackass Rabbits of Salt Lake Valley, Utah, were 

 nearly exterminated by a fatal disease, their dead bodies being found 

 scattered over the plains in great numbers. From being so common 



