HESPEROMYS. 145 
defined by Dr. Coues as having usually a proportionally shorter tail and a less 
rufescent coloration than the typical H. leucopus of the Eastern States; but the com- 
parison of an immense series of specimens in the United-States Museum has 
enabled him to show that these characters are very far from being constant, and that 
they cannot be regarded as marking even a pure geographical race; “ for undoubtedly 
leucopus occurs throughout the United-States range of ‘sononiensis, and everywhere 
the intergradation is perfect”. 
The exact southern range of the White-footed Mouse remains to be traced ; but it 
certainly extends far into Mexico. Sallé’s collections in the British Museum include 
an example of the sonoriensis variety, labelled ‘‘South Mexico ;’” and another of the true 
leucopus phase is from Oaxaca. In the warmer lowland regions of the republic, 
however, it is probably replaced by the next species, H. aztecus. 
Of the habits of the White-footed Mouse in Northern Mexico Mr. J. A. Clark 
observes that ‘‘ This animal seems to live, as circumstances may determine, either on 
the ground or in the hollows of trees... .. This or an allied species builds globular 
nests of fine grass, lined with feathers and other soft material, on the opuntia and 
other chapparel. They are quite numerous in some sections, and, seen at a distance 
hanging on thorny branches, resemble old bird-nests. The entrance, usually at the side 
or bottom, is to all appearance so entirely closed as to suggest the question, By what 
built, or for what purpose, is such a contrivance? I never saw one in an unfinished 
state, nor the animal at work; labour is perhaps performed after nightfall” ’. 
8. Hesperomys aztecus. 
Hesperomys aztecus, de Saussure, Rev. et Mag. Zool. 1860, p. 105, pl. ix. fig. 4 (descr. orig.)’. 
Hesperomys (Vesperomys) aztecus, Coues, Proc. Ac. Philad. 1874, p. 180°; Mon. N.-Am. Rodent. 
p. 100°. 
Hab. Norvu America, California ?.—Mexico (de Saussure’, U.S. Nat. Mus.*). 
The specific distinction of the Aztec Mouse of M. de Saussure has been lately con- 
firmed by Dr. Coues, the Smithsonian Institution having received spirit specimens 
collected at Cape St. Lucas, California. Besides the rich rusty red of the flanks of the 
adult (for the young appear to be grey like those of H. leucopus), the species may be 
recognized by the extension of the darker colouring to the basal third of the meta- 
tarsus and by the long, nearly naked, and almost unicolorous tail. Dr. Coues observes 
that “there is no reasonable doubt that the animal is a subtropical offset of H/. leucopus, 
inodified just as Neotoma ferruginea has been [from NW. fuscipes|; but, at the same time, 
the differentiation has proceeded so far that we are bound to place the animal on 
specific footing, at any rate until intermediate specimens are forthcoming”. ‘Till 
then, also, we can say nothing as to the distribution of the species in Central America, 
the only known Mexican specimens being without exact localities. 
BIOL. CENTR.-AMER., Mamm. Vol. 1, August 1880. U 
