480 U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENEKAL REPORT. 
leucopus ; they are thin, membranous, and sparsely clothed with scant hairs. The tail is very 
long, considerably exceeding the body; it is more finely annulated than in H. leucopus, and 
covered with hairs, which, however, do not conceal the annuli. 
The hair of this species is quite long, though not particularly soft. The upper parts are of a 
light grayish yellow, finely lined by the black tips of the hairs; the cheeks and lower part of 
sides with rather a distinct stripe of light ochrey yellow. The under parts and the feet are 
pure white; the tail is uniform in color, or, at most, a little lighter beneath, the line of sepa- 
ration entirely inappreciable. : 
The colors of this species are more yellow, and much lighter, in every way, than in H. 
leucopus. It is much smaller and lighter colored than H.°californicus, in which we have 
similar characters of naked soles, very long and unicolor tail, &c. 
List of specimens. 
Measurements. 
Seal 3 = i a Exaa) See es 
adi ona #/£is)2 
a s a 2 
E ites a Locality. When Whence and how Nature of . 9 3 Sa es = g Collected by— 
Se ey collected. obtained. specimen. | 2] 8] 8 |! | Sales 
= tp o o eo ° =] | = =) S| S + 
Ege lies ie Ph Persie Paci ere fae eae pees =A bess 
Ss 7 = = J - = [-} S = s = 
= 2S ] o o o ROA AS to | & | ‘ep 
= | Belts s é/6|/6)|6 E a|s|5/\%s 
o | 5 la zi2l2/42lelel/a]/a/s 
| | eS ae ee SS aa | | | — |e 
1581 | 2416 | @ | Fort Yuma, Cal......] 1853......... Maj. G.H.Thomas. Skin ...... coor |ooe{L.08/3.17-4,08/4.25)....] -76 ....| aeeene eesenceece 
ROLE wissen) ase n]avsce's GO. cevecccvcess o1GOs. voe.sceleveveces do.....s0c0| Imiale..... 48 +95/1.07 Rae BakOl cece} 00). G0) <GD) voce mn\cmemnnieaen 
SRI) acecaleee-| <a ces gts Me «toare ont Sdor,.s cueecles sacs dbsspeaser etsy dois acs .42| ,85)1.00}2.583.14)....| .30) .80 .66|.......0000+ ae 
1334 | Colorado bottom, Cal. | Feb. 24, 1855 | Maj. W. H. Emory. Skin..... aeleweh fe } 
1835) | Gcocie|eindg) pencur dhoonpapseisaes Ef tehoney Cilhga| ce ceeas dO... us oats sen lac dOssieweans Ben CeOAl 
13S6 | veeeee cece |seeees Ovecenvre veces NeOnr clan dO... }aecsceee dO.sceeveces ve Oss cccccsjever|oaes | 
| \ { 
HESPEROMYS (ONYCHOMYS) LEUCOGASTER. 
Missouri Mouse, 
Hypudaeus leucogaster, Prinz Max. Reise in das innere Nord-Amerika, II, 1841, 99. (Fort Clark.) 
Mus Missouriensis, Aup. & Bacu. N. Am. Quad, II, 1851, 327; pl. c. 
Sr. Cu.—Color above, grayish brown, passing into yellowish red, and finally into a stripe of fulvous on the sides. Feet, 
including outer surface of the fore arm and under surface of the body and tail, white. For generic characters see page 458. 
This species, in some respects, bears a resemblance to Arvicola, especially in the short tail, 
and rather short ears ; it is in general appearance, however, nearer to the ordinary white-footed 
mice. Still, in many respects, there is a striking difference from both, to be hereafter 
referred to. 
The head is proportioned much as in Hesperomys leucopus, though with a broader muzzle ; the 
muzzle is entirely hairy, except on the septum; there is rather more hair than in H. leucopus. 
The lip is cleft nearly to the septum. The eyes are large, the whiskers long, and white and 
black. The ears are small, about two-thirds the height, and half the area of H. leucopus. The 
antitragus is low and very slightly valvular, less so than in H. leucopus. The membrane is 
rather thick, the surfaces of the ear well coated with short hairs, longest on the convexity, and 
nearly naked around and anterior to the meatus, 
The most conspicuous feature of this mouse is in the peculiar proportions of the limbs. The 
