RODENTIA—MURINAE—HESPEROMYS SONORIENSIS. A75 
Although I have not the slightest doubt that this species is distinct from H. leucopus, I have 
been unable to decide whether it is different or not from the mouse from Sonora, characterized 
as H. sonoriensis by Major Leconte from specimen 146 of the Smithsonian collection. This was, 
however, not quite mature, and more perfect specimens, collected by Dr. Henry at Fort Thorn, 
enable me to give the peculiarities of the animal with more precision, as follows: 
Sp. Cu.—Size larger than IZ leucopus. Body stout. Ears very large, rather densely coated with long appressed hoary 
hairs. Tail much shorter than the body or about two-thirds this length. 'Tarsi short. Above, mixed gray, lead color and 
yellowish brown, without any reddish tints whatever. 
Size larger than that of the typical Mus leucopus of the east. Fur soft and short. Body 
very stout and full. Ears very large and broad, the outer surface covered with depressed hairs 
on their posterior half. Tail unusually short. scarcely reaching to the occiput when bent over 
the back ; the vertebree very stout and tapering rapidly to the tip. Hind feet rather short. 
The prevailing color above is a mixed gray, dark brown, and pale yellowish brown; the 
dark brown predominating on the back, the gray on the sides. The single hairs on the back 
are dark lead color, with a light grayish end terminated by very faint yellowish brown. On 
the sides the gray is very distinct, becoming obsolete towards the back. In fact, there is a 
decided hoary tinge above. The under parts of the body, the feet, including the entire fore 
arm, and the tail, except a dusky surface above, white. The extreme tip of the tail is formed 
by white hairs. The ears are dusky, becoming hoary towards their margin on both surfaces. 
The young of this species, after immersion in alcohol, are of a rather dark slate color above 
and on the sides. 
It will thus be seen that the general characteristics are very similar, proportions, coloration, 
&c., the only differences now appreciable being in the considerably larger size of the skins of 
the Sonora and New Mexican animals. Though this would give some color to a distinction of 
species, I do not feel authorized to impose a new name without further data, especially as the 
regions inhabited by the H. sonoriensis are, zoologically, very much the same with the Upper 
Missouri. It is quite possible, too, that if the largest of the Missouri specimens catalogued 
had been skinned when fresh, and then somewhat stretched in stuffing, they would have been 
little inferior in size to those from Fort Thorn. 
The Mus leucopus of Richardson appears to be the same with the H. sonoriensis, and if all the 
other specimens quoted below are the same, it will indicate a very extensive range, from Sonora 
along the Rocky Mountains and Black Hills to the Saskatchewan, or even further north 
