152 GLIRES. 
As I have elsewhere pointed out °, this species was named by Gray in 1843 ', but, as 
he gave no description, M. de Saussure’s title will stand. The latter author subse- 
quently described a second Mexican species as Reithrodon sumichrasti®; but it is 
impossible to distinguish it by the characters given, and I am convinced that it is 
merely founded on an unusually brightly coloured example of O. mexicanus, which 
seems to gain a greater brilliancy of tint in the more southern parts of its range. 
Some of Mr. Salvin’s Guatemalan specimens were referred by Mr. Tomes to 0. longi- 
cauda (Bd.); but I have been unable to confirm his identification, and agree with 
Dr. Coues in feeling great doubt as to the existence of that species in Central America. 
Nothing special has been recorded of the habits of this species, which doubtless 
resemble those of the last named. Dr. Coues remarks that one of the specimens of 
O. mexicanus in the Washington Museum “ is a perfect albino, pure white everywhere, 
and doubtless had pink eyes”’. 
4. SIGMODON. 
Sigmodon, Say & Ord, Journ. Acad. Philad. iv. p. 852 (1825). 
The generic distinction of the Cotton-Rat from the other American Mice has been 
generally recognized, though Dr. Coues has latterly expressed doubts as to its being 
more aberrant than some of the subgenera of Hesperomys*. ixternally it may be best 
distinguished from the subgenus Oryzomys by its blunt muzzle, large ears, and long 
hind feet, of which the first and fifth toes are subequal and very short. In the skull 
the perpendicular plate of the zygoma is emarginated, the supraorbital ridges well 
marked and sharp, and the incisive foramina long. The molars are usually stated not 
to be tuberculate at any age (Dr. Coues says the tubercles are lost so early that he has 
not been able to observe the primitive unworn condition) ; and the indenting enamel- 
folds are deep and closed, usually giving a somewhat imperfect sigma pattern on the 
crown of at least the posterior teeth, and thus suggesting the mame of the sae of 
which only one species appears to be well established. 
1. Sigmodon hispidus. 
Sigmodon hispidum, Say & Ord, Journ. Ac. Philad. iv. p. 354, pl. x. (1825, descr. orig.)*. 
Sigmodon hispidus, Baird, Mamm. N. Am. p. 5027; Coues, Proc. Ac. Philad. 1874, p. 176°; Mon. 
N.-Am. Rodent. p. 36%. 
Sigmodon berlandieri, Baird, Proc. Ac. Philad. 1855, p. 838 (deser. orig.)°; Mamm. N. Am. p. 504°; 
Rep. U.S. Mex. Bound. Surv. ii. Mamm. p. 467; Tomes, P. Z.S. 1861, p. 281°. 
Hesperomys (Deilemys) toltecus, de Saussure, Rev. et Mag. Zool. 1860, p. 98, pl. 10. figs. 8, 3a 
(descr. orig.)’. 
Hab. Norra America, from South Carolina southwards 4.—Mexico (Cuming, Warwick, 
* Mon. N.-Am, Rodent. p. 32. 
