500 



U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



In this specimen of Dr. Suckley's I, without difficulty, recognized the original Myaxus drum 

 mondii of Dr. Richardson, so different from the animal given by Audubon and Bachman. It 

 is hardly possible that the distinctions between this skin and those collected by Mr. Townsend 

 on the Columbia, and which served as the basis of the descriptions of Audubon and Bachman, 

 can be less than specific. Four specimens of this N. occidentalis, one of Mr, Townsend's original 

 specimen and three sent by Dr. Cooper, agree in all points, and were collected, respectively, in 

 the months of June, September, and October ; Dr. Suckley'a in August, a period covered by 

 that of the others. The fur of the present species is very much softer, both above and below ; 

 the tail shorter, with more white on the sides, less brown above, and the coarse wool at the 

 base lighter gray. The ears are larger. The color above is a very light yellowish brown or 

 fawn, instead of a brownish lead color mixed with a little yellowish brown. A comparison of 

 the portion of the skulls remaining in the skin exhibits important differences. The molars are 

 decidedly broader, though of the same aggregate length ; the hinder one shorter and more con 

 densed. The shape of the lower jaw is decidedly different ; it is much shorter and more mas 

 sive, thicker below the molars, the symphysis longer and stouter, the body deeper, and in every 

 way calculated for greater strength. 



A skin received from Dr. Hayden, since the above description was prepared, and collected on 

 the Yellowstone, agrees in all essential characters. 



This species was first mentioned and very accurately described by Lewis and Clark, from 

 a specimen taken near the falls of the Missouri, who, however, imposed no scientific name. 

 This was done in 1815, by Ord, in his little known list of the animals of North America, in the 

 second American edition of Guthrie's Geography. In 1828, it was called Myoxus drummondii, 

 by Richardson, from its close resemblance to that genus. Subsequently, however, an examina. 

 tion of the teeth showed him that it belonged to Neotoma. The species described by Audubon 

 and Bachman as N. drummondii belongs to quite a different species, (N. occidentalis.') 



List of specimens. 



