MURIDAE— SIGMODONTES— I1ESPEROMYS. 43 



Genus HESPEEOMYS, Waterhouse. 



XMlls, Bp., AUCTOEUM. 



X -Irricola, sp., Harlan, Am. Monthly Jonru. 1832, 446 (nutialli). — Aur>. & Bach., Q. N. A. (sononensis, 

 LeC; lexana, Woodb.; and oryzivora, And. & Bach. = ilfug paluttris, Hail.}. 



Xllypiulams, sp., Maximilian, Reise, &c. ii, 1641, 9!) (ZT. leacogaster, Max. = Mus niissourknsls, Aud. &, 

 Bach.). 



> Mnsculus, Katinesque, Aid. Monthly Mag. iii, 1818, 44(i (type, M. Jeucopus, Eaf. !). 



< Hesperomys, Waterhouse, Zool. Voy. Beagle, 1839, 75 (established to accommodate the New World 

 mice collectively, aud therefore equivalent to the tribe Sigmodontes as uow understood). 



> Cahnujs, Aud. & Bach., Q. N. A. ii, 1851, 303 (aurwlim). (Not of Waterh.) 



> Oiiychomys, Baird, M. N. A. 1857, 458 (type, Hypudaus leueogaster, Max.). 



> Orysomys, Baird, op. et loc. cit. (type, Mus palustris, Had.). 



> Yesperimns, Codes, Proc. Acad. Nat. Sci. Phila. 1874, 178 (type, S. 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 Murince, collectively, from the typical Mures of the Old 

 "World, upon the broad character of the tuberculatum 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 Slg?nodon certainly belong to the same group." It is 

 plain, therefore, that his "genus" Hesperomys is precisely equivalent to the 

 "tribe," or supergenus, now called Sigmodonles. 



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.), Habrotltrix, PhyZlotis, 8capteromys, 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- 



