Rcisc, ii. 1841, 99 (leucogafder). — Muf>culuii , Raf., Am. Monthly 

 3Iag. iii. 1818, 446 (^leucopua). — Hei^peromyn^ Waterh., Zool. Voy. 

 Beag. 1839, 75 (established for the New World mice collectively, and 

 therefore equivalent to the tribe Sigmodontea as now understood). — 

 Calomys, Aud. and Bach., Q. N. A. ii. 1851, 303 (aureolus). — 

 Onychomys, Bd., M. N. A. 1857, 458 {leucogaster, Maxim.). — Ory- 

 zo7nys, Bd. op. et loe. cit. {palustris Harl.). 



aud Neotoma. Naturalists -soon perceived the supergeneric value of this 

 assemblage, and sought to eliminate various groups under other generic 

 appellations. Waterhouse liimself established a number of divisions which, 

 with some modifications, have been generally accepted. In North America, 

 Sigmodon and ]Yeotom((, with the so-called ^^BeitJu-odon,''^ stand well apart 

 from Uesperomys ; in South America, Holocheilus and the true ReitJirodon 

 seem perfectly distinct. The rest of the American mice (at least so far as 

 I know them) most probably fall under a restricted genus Het^peromys; 

 we have only to tie this name down to the strict value of a genus, pin it to 

 its type, and establish among the numerous species what subgeneric divi- 

 sions we can. From the circumstances of its founding it is difficult to say 

 what should be considered the type of He'^peromys. Waterhouse, in drawing 

 his comparisons between Mus and the New World mice, took 31. rattus and 

 M. bimaculatua for such purpose ; we may properly therefore elect the 

 latter as technically the type. But when Waterhouse, in 1837, established 

 Calomys upon G. elegans, he included in it both Mmaculatus and gracilipes ; 

 and Eligmodontin of F. Cuvier is strictly coequal. It becomes a question 

 whether one of these names should not stand in place o^ He'^peromys as re- 

 stricted ; but as the latter is firmly established, as Calomys is by tlie same 

 author, and as Eligmodontia is no earlier, there may be no necessity for a 

 change. Resting then upon this strict application of HesperomyH to such 

 species as bimaculatui^, elegans, aud gracilipes, we may inquire how nearly, 

 if at all, the North American Vesper-mice agree with it. In his essay of 

 1857, Prof. Baird elaborately details the characters of the South American 

 species, and, excluding Reitlirodon and Holocheilus as full genera, makes 

 He>(peromy» to include three subgenera, viz., Calomys Waterh., HdbrotJirix 

 {=:niibrot?inx plus PJiyllotis, Waterh.) and Oxymicterus (^=Oxymictems 

 plys Scdpteromys., Waterh.). Among North American forms, he establishes 

 three subgenera, Hesperomys, OnycJiomys, and Oryzomys. I confirm these 

 last unequivocally ; the only point being whether the leucopus group, which 

 Baird left in Hesperomys, is not also a group subgenerically different from 

 that including elegans, bimnculntus, etc. All the North American mice 

 seem to be differentiated from those of South America by characters of 

 more than specific importauce ; the closest approach that I am aware of 

 being found in the leucopu!^ group, a species of which — mittalli, yellowish 

 underneath — comes near Gdlomys. 



I propose to retain Uesperomys for all the North as well as certain South 

 American species, and to divide the former into three subgenera; Vesperimus, 

 Mihi. Onychomys, Baird, and Oryzomys, Baird. 



