13 



GEOMYID^. 



25. Thomomys rufescens Maxim. Fort Union Gopher. 



The little mounds of earth thrown up by some species of Thomo- 

 mys were frequent in the moister parts of the prairies east of the 

 Yellowstone, but were more rare along the Yellowstone, and still less 

 jrequent along the Musselshell. The only specimen obtained was 

 taken on the Yellowstone, near Camp Thorne. 



CASTORID^. 



26. Castor fiber Linn. Beaver. 



Sparsely distributed along all the principal streams. Along the 

 Yellowstone indications of their presence were seen at only a few 

 points. 



SCIURID/L. 



27. Sciurus hudsonius Pall. Red Squirrel. 



One or two were seen on the Musselshell, among the pines that 

 cover the sandstone ridges. 



28. Tamias quadrivittatus var. pallidus All. Missouri 

 Striped Squirrel. 



Rather frequent from the Little Missouri westward, especially in 

 the bad lands along the Yellowstone and the sandstone bluffs of the 

 Musselshell. Nowhere, however, very abundant. 



29. Spermophilus tridecem-lineatus var. pallidus All. 

 Striped Gopher. 



Generally distributed, but much more numerous on the prairies 

 east of the Yellowstone than in the Yellowstone valley, or west of it. 



30. Cynomys ludovicianus Bd. Prairie Dog. 



More or less generally distributed throughout the region traversed, 

 but nowhere very numerous, and sometimes not seen for days to- 

 gether. 



HYSTRICID^E. 



31. Erethizon dorsatus var. epizanthus All. Porcupine. 

 Rather rare. Two specimens were killed near the Heart River, 



and indications of their presence were seen elsewhere. 



