500 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT: 
In this specimen of Dr. Suckley’s I, without difficulty, recognized the original Myoxus 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 NV. 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’s 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 NV. drummondit belongs to quite a different species, (JV. occidentalis.) 
List of specimens. 
Measurements. 
5 2 = 
: % 5 | 3 gz =} 
2\* a} |e 1212 [a he 
§ 6 Locality. Whencol- | Whence and how| & Le 5 = “3 = Collected by— 
A | lected. obtained. a = ee = 5 
o a a = we ay o 
z po S s = = -) ro) > 
& o 2 = | 9 3 = | 2 
2|& Se ae a oe 
3s S os 6 | 3 ‘3 o a a 
o o z yf 5! B i 4 a 
224 | 1694 | Milk river, Nebraska.......... Aug. 26, 1853 | Gov. I. I. Stevens..| Skin...| 7.75 5,00 | 5.83 | 1.42 |...... 1,00 | Dr. Suckley, U.S.A. 
1331 | 2159 | Fort Sarpy, Yellowstone river.| Aug. 1854 | Col. A. Vaughan...|..do....| 7.00 4.00 | 4.50 | 1.42) 1.75 .90| Dr. F. V. Hayden... 
