RODENTIA-MURINAE-HESPEROMYS GAMBEL1I. 
465 
Color. —Above, mixed glossy brown and yellowish brown, tbe former predominating on tbe 
back. Sides but little paler. Ears dusky. Tbe white of the fore leg extending as far as tbe 
elbow. Under parts and feet white. Tail white, dusky above ; tbe difference of color very 
evident. 
Several specimens of Hesperomys were caught at Posa Creek by Dr. Heermann, differing in 
some respects from tbe others brought in from tbe west by exploring parties. As they appear 
not quite grown, I hesitate about describing them as new, and, for the present, at least, prefer 
to place them under H. gambelii. 
This species differs from H. boylii in the much shorter tail and less number of caudal verte¬ 
brae, more villose ears, with longer fur at their inner base on the top of the head, shorter hind 
feet, &c. 
This species, in size and general appearance, represents very closely the Hesperomys leucopus of 
the eastern States to such a degree, in fact, that as yet I have not found any easily expressed 
characters to distinguish them. There is the same plumbeous hue in the young, the yellowish 
brown of the back, &c. I do not find, however, a tendency to a distinct darker stripe on the 
middle of the back, as in H. leucopus , and the general appearance of a series of each is quite 
different. It is barely possible that my H. austerus may be a northern variety of the common 
Californian species, of smaller size and darker color, somewhat like the gray and smaller H. 
leucopus of Nova Scotia, and probably Labrador. The differences, however, are considerable, 
and further materials will be necessary to decide the question. 
List of specimens. 
59 L 
Possibly H. boylii. 
