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MURIDAE—SIGMODONTES—HESPEROMYS. 43 
GENUS HESPEROMYS, Waterhouse. 
x Mus, sp., AUCTORUM. 
x Arvicola, sp., HARLAN, Am. Monthly Journ. 1832, 446 (nuttalli).—Aup. & Bacu., Q. N. A. (sonoriensis, 
LeC.; tecana, Woodh.; and oryzivora, Aud. & Bach. = Mus palustris, Harl.). 
X Hypude@us, sp., MAXIMILIAN, Reise, &e. ii, 1841, 99 (1. leucogaster, Max. Mus missouriensis, Aud. & 
. Bach.). 
> Musculus, RAVINESQUE, Am. Monthly Mag. iii, 1818, 446 (type, MZ. leucopus, Raf.!). 
< Hesperomys, WATERHOUSE, Zool. Voy. Beagle, 1839, 75 (established to accommodate the New World 
mice collectively, and therefore equivalent to the tribe Sigmodontes as now understood). 
> Calomys, AuD. & Bact, Q. N. A. ii, 1851, 303 (aurcolus). (Not of Waterh.) 
> Onychomys, BAIRD, M. N. A. 1857, 458 (type, Hypudwus leucogaster, Max.). 
> Oryzomys, BarRD, op. et loc. cit. (type, Mus palustris, Harl.). 
> Vesperimus, CouEs, Proc. Acad. Nat. Sci. Phila, 1874, 178 (type, H. leucopus). 
In proposing the name Hesperomys, Waterhouse’s idea, as is evident 
throughout his article in the Zoology of the Beagle, was simply to separate 
the New World Murine, collectively, from the typical Mures of the Old 
World, upon the broad character of the tuberculation of the molars, which is 
biseriatim in the former and triseriatim in the latter. Although treating 
exclusively of the South American species, he says in one place, ‘ Mus leu- 
copus, Neotoma, and Sigmodon certainly belong to the same group.” It is 
plain, therefore, that his genus” Hesperomys is precisely equivalent to the 
“tribe,” or supergenus, now called Sigmodontes. 
In a word, “ Hesperomys” is a tribal name, comprehending in itself the 
genera and subgenera that here follow: A, in South America, Calomys 
(= Eligmodontia, F. Cuv.), Habrothrix, Phyllotis, Scapteromys, Oxymicterus, 
Holochilus, Reithrodon ; and, B, in North America, Vesperimus, Onychomys, 
Oryzomys, Ochetodon, Sigmodon, Neotoma. 
Almost from the very first, naturalists perceived the heteregeneous char- 
acter of this assemblage under the comprehensive term Hesperomys, and 
sought to eliminate proper generic groups. Waterhouse himself made a 
number of subdivisions, which, with some modification, have been generally 
accepted. It is a matter of obvious necessity to restrict Hesperomys, and so 
define it that it shall designate a homogeneous group. ‘To do this, we have 
first to throw out the forms worthy of generic separation, then to mark out 
the subgeneric divisions of Hesperomys, and finally to tie down the name in 
its strict sense to the species upon which it is based. 
From the circumstances under which Hesperomys was instituted, and the 
author’s evident intention in founding it, it is difficult to say what should be 
considered as his type-species; really, he had no type in view. But, in draw- 
