100 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



rather fall under t lie sonoriensis category by reason of (he shortness of the 

 tail. There is little to note regarding these specimens. No. 718G, from Fort 

 Mojave, is about the palest fulvous all over the upper parts we have seen, but 

 still is not at all like eremicus. No. 7183 is almost a typical leucopus. The 

 two adults of the Tejon series have almost exactly the body-colors of gossi/- 

 pinus : and we should not omit to note that they have a suspicious sort of 

 resemblance to II californicus. Nor should we be surprised if some mice 

 from this vicinity should be found to bridge over the chasm that now appears 

 between the leucopus styles and the seemingly very different "californicus"; 

 one, at least, of the Tejon specimens (No. 3670) being veritable californicus. 

 Wc have already noted that Northern Californian mice, and more particu- 

 larly ( Oregon and Washington ones, are darker than those of Southern Califor- 

 nia (in this respect precisely matching Massachusetts leucopus), and that 

 they shade directly into austerus in this respect, as well as in the length of 

 the tail. 



HESPEROMYS (VESPERIMUS) AZTECUS, De Saussure. 



Aztec Mouse. 



Hesperomys aztecus, Dk Saussure, K. M. Z. 18G0, 105, pi. ix, f. 4 (teeth). 

 Hesperomys ( Vesperimus) aztecus, Coues, Proe. Acad. Nat. Sei. Phila. 1ST4, 160. 



Diagnosis. — II. leucopo staturd par, et forma simillimus, sed caudd sub- 

 niuld ct coloribus differt. Brunneus, do/so nigricante, lateribus ferrugineis, 

 partibus inferioribus albis ; antebrachio extus lateribus concolore, crure et parte 

 tertia basali metatarsi fuscescentibus ; caudd fere unicolore. 



Habitat. — "Mexico" (De Saussure). 



This species belongs strictly to the Hesperomys leucopus group,* and does 

 not differ noticeably in size or proportions from that species. The coloration, 

 however, appears specifically distinctive; it differs from that of the ordinary 

 United States species precisely as Neotoma ferruginea differs i'vomjloridana. 



The upper parts are rich rusty-red, almost orange rust-color, on the 

 back deepening into a broad area of brownish-black, and only showing in its 

 intensity on the sides where the line of demarkation with the white of the 

 under parts is distinct and sharp. The head shares somewhat of the general 

 blackening of the middle area above, but is not so uniformly dark as the back ; 

 the extreme muzzle is dark, leaving about the mouth only the sides of the 



* In all external features, at any rate. ; but wo have not ascertained the existence of chcek- 

 poncbes. 



