MURIDAI—SIGMODONTES—HESPEROMYS AZTECUS. 101 
lips to share the white of under parts; the latter is not quite pure, owing to 
the showing through of the gray bases of the hairs. On the fore leg, the 
color of the sides, or a darker shade, extends to the very wrist, there stopping 
abruptly, leaving the surface of the paw white (or light). On the outside of 
the crus, the color of the sides, or a deeper shade, extends to the tarsus, and 
thence on the basal third of the metatarsus; forming a sharply-defined blackish 
area, as in H. sumichrasti, &c. This is a strong feature that never occurs in 
true dewcopus ; the rich rusty-red of the sides is likewise an entirely peculiar 
shade so far as United States mice are concerned, though common to several 
Mexican species. The ears are dusky in the present state uf our specimen ; 
the tail, of which less than two inches remains on the specimen, is very 
obscurely paler below and nearly as naked as in A/uws; but this last feature 
may not be permanent. 
The foregoing is the adult coloration. We have no information whether 
the young are like the adult, or plain gray like young dewcopus. 
Length, about 3.75 inches (0.095, De 8.); tail, averaging over 4.00; 
hind foot, 0.90; fore foot, 0.88; ear, about 0.62 high from notch in front. 
Described from one of the three original specimens, No. 8926, Museum 
of the Smithsonian Institution, received from M. De Saussure, and labeled in 
what is apparently his handwriting. 
M. De Saussure’s label bears the suggestive query, ‘H. texanus??” There 
is no reasonable doubt that the animal is a subtropical offset of H. deucopus, 
modified justas Neotoma ferruginca has been; but, at the same time, the differ- 
entiation has proceeded so far that we are bound to place the animal on spe- 
cific footing, at any rate until intermediate specimens are forthcoming. 
Since writing the foregoing, we find, as stated in another place, a number 
of alcoholic specimens, undoubtedly referable to this species, among a lot of 
leucopus (gambeli) from Cape Saint Lucas. The fact that these examples are 
instantly distinguishable strengthens the probabilities of the permanent dis- 
tinctness of aztecus from any of the United States varieties of deucopus. 
They all show a nearly naked and almost unicolor tail, and the peculiar exten- 
sion of the dark color on the base of the metatarsus. A suckling young 
appears to be gray, like young dewcopus, as was to have been anticipated. 
We cannot make out, in the alcohol, whether or not the peculiar richness 
of the ferrugineous, with very black dorsal area, exists or not, the wet speci- 
mens being indistinguishable in body-colors from the ‘“gambeli” that came 
