MURIM3— SIGMODONTES— HESPEROMYS AZTECUS. 101 



lips io 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 cms, 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 leucopus ; 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 Mus ; 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 leucopus. 



Length, about 3.75 inches (0 mm .095, Do S.); tail, averaging over 4.00 ; 

 hind foot, 0.90 ; fore foot, 0.38 ; car, about 0.G2 high from notch in front. 



Described from one of the three original specimens, No. 3926, 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, U H. texanus'i '?" There 

 is no reasonable doubt that the animal is a subtropical offset of H. leucopus, 

 modified just as Neotoma ferrug'mea 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 leucopus. 

 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 leucopus, 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 



