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U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—“GENERAL REPORT. 
HESPEROMYS MYOIDES. 
Hamster Mouse. 
Cricetus myoides, Gapper, Zool. Jour. Y, 1830, 204; tab. x. 
? Mus leucopus, Thompson, Nat. Hist. Yt. Appendix, 1853, 13. 
? Ilesperomysgracilis, Leconte, Pr. A. N. Sc. Phila. VII, Dec. 1855, 442. 
Sp. Ch. —Size of H. leucopus or larger. Tail vertebra generally .25 of an inch longer than bead and body, with a decided 
pencil at the end. Jaws with moderate cheek pouches. Color above, cinnamon brown, lined with dusky; ears and upper 
part of tail, similar. Under parts and feet, pure white, the color extending over the whole fore leg. Immature speci¬ 
mens fuscous, much as in H. leucopus. 
My attention was first called to tliis species by noticing that all the white-footed mice from 
near Burlington, Vermont, had much longer tails in proportion than those from Middlehoro’, 
Massachusetts. It then occurred to me to see if the former were in any way related to the 
Cricetus myoides of Gapper, and, much to my astonishment, I found decided indications of 
cheek pouches in all the alcoholic specimens examined. I then investigated a considerable 
number of Middlehoro’ specimens, and in none could I detect the slightest indication of 
anything of the kind. 
These pouches are not very deep in the alcoholic specimens, as might naturally he expected 
from the highly contractile character of their walls. In fresh specimens, according to Gapper, 
they extend to the ear ; here, however, they only reach hack as far as the posterior edge of the 
eye, or about .30 of an inch from the edge of the mouth. They open on each side of the fleshy 
palate, between the incisors and the molars, and pass obliquely backwards. The walls are 
thickened and corrugated, probably by immersion in alcohol; naked, or with a scattered hair 
here and there. In the bottom of one were a few hits of a blackish substance. 
In external appearance there is very little to distinguish this species from H. leucopus from 
Middlehoro’. The ears are very similar, except, perhaps, a little narrower and higher, 
and less rounded above. The antitragus is long and quite well developed. The nose and feet 
are precisely similar, except, perhaps, that the tubercles of H. myoides are larger. The tail 
only is generally longer than the head and body instead of being shorter. It has also a long 
pencil of hairs at the tip. 
I fear I shall find it quite difficult to define this species so that it will be recognized without 
anatomical examination. The colors, however, differ in some points from those of H. leucopus, 
resembling more those of E. aureolus. I have never seen so vivid a yellowish brown in 
H. leucopus as pervades the upper parts of H. myoides. There is more or less of a dusky band 
along the back, not so conspicuous, perhaps, as in E. leucopus. In the only two adult or red 
colored specimens before me the membrane of the ear and the upper part of the tail, instead of 
being fuscous brown, are yellowish or cinnamon, a feature not seen in the other. In the more 
plumbeous or grayish young, however, this character is inappreciable. The entire under parts 
of body and tail and the feet are snowy white, the line of demarcation passing high up on the 
sides, leaving the whole outside of the fore leg white. 
More immature specimens, instead of the yellowish brown, are more fuscous, as in the 
H. leucopus , the dusky color extending even to the wrist. 
As far as I can discern there is nothing whatever in the skull and teeth of this species in 
any way different from that of Eesperomys leucopus. It bears no resemblance to that of 
Cricetus, and as the only common character lies in the mutual possession of cheek pouches, it 
