M'CHESNEY on DAKOTA MAMMALS. 



211 



to think separation of the two species could be made by coloration 

 alone, viz, by the darker appearance of A. riparius both on the back 

 and belly, and by the black legs and feet, and such may possibly be done 

 to a small extent, especially with extremes of the two species ; but the 

 coloration was soon found to intermingle to such an extent that exam- 

 ination of the molars alone would determine to which species the speci- 

 men belonged. 



The tails were found to vary fr«m distinctly bicolor to almost entirely 

 black. 



The backs varied from dark brown to a decidedly reddish cast ; some 

 were also nearly grizzly-gray. 



The under parts varied from silvery-gray to dark brown. 



The legs and feet varied from black to almost white. 



Fiber zibethicus, {Linn.) Cuvier. 



The Mnskrat is the most abundant of all the mammals inhabiting this 

 region. As many as twenty thousand have been taken in a single season 

 within a few miles of this post. 



SACCOMYID^. 

 Cricetodipus flavus, Baird. 



The Yellow Pouched Mouse is found in small numbers in this region. 

 Specimens taken are a little larger than those enumerated by Baird. 



List of specimens. 



GEOMYID^. 

 Geomys bursarius, Slmw. 



The Pouched Gopher is one of the most abundant of all the mammals 

 inhabiting the prairie of this vicinity. I certainly disagree with those 

 authorities (and my opportunities for forming a correct opinion have 

 been as great as, if not greater than, any former observer's) who believe 

 that the cheek-pouches of this mammal are used for the removal of sand 

 from their burrows; for in all the numerous specimens taken here, no 

 earth has ever been found in their pouches, but, on the contrary, I have 

 frequently found young grass, leaves, and roots in their pouches, and I 

 believe that the succulent young grass, when procurable, frequently con- 

 stitutes their main article of food. It might be objected that my speci- 



