NATURAL SCIENCES OF PHILADELPHIA. 17T 



Reise, ii. 1841, 99 (J,exi,cogaster).Mmculm, Raf., Am. Monthly 

 Mag. iii. 1818, 446 (leucoptii^).IIe!<peromyx, Watcrh., Zool. Voy. 

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

 therefore equivalent to the tribe Sigmodontes as now understood). 

 Calomys, And. and Bach., Q. N. A. ii. 1851, 303 iauveolu><). 

 OnycJiomys, Bd., M. N. A. 1857, 4r)8 {leucogaster, Maxim.). 0/'^- 

 zomys, Bd. op. et loc. cit. {palustvis Harl.). 



and Neotoma. Naturalists soon perceived the supergeneric value of this 

 assemblage, and sought to eliminate various groups under other generic 

 appellations. Waterhouse himself established a number of divisions which, 

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

 Sigmodon and Neotoma^ with the so-called ^'Eeithrodo}},'' stand well apart 

 from He>iperomys ; in South America, Ilolocheilus and the true Reithrodon 

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

 I know them) most probably fall under a restricted genus Ilesperoinys; 

 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 subgeueric divi- 

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

 what sliould be considered the type of IIe>iperomys. Waterhouse, in drawing 

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

 If. bimaculatus for such purpose ; we may properly therefore elect the 

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

 Calomya upon C. elegdns, he included in it hoih bimaculatm ?md gracilipes ; 

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

 whether one of these names should not stand in place of IIe^j}eroiirys as re- 

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

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

 change. Resting then upon this strict application of Hes^peromys to such 

 species as binD/culatus, elegnm. and gnicilijyes, 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 Beithrodon and Ilolocheilus as full genera, makes 

 Heqjeromys to include three subgenera, viz., Calomys Waterh., ILibrotlirix 

 {z=Habrothrix plus Phyllotis, Waterh.) and Oxymieterus (=:Oxymicterus 

 plus Scupteromys, Waterh. ). Among North American forms, he establishes 

 three subgenera, Hesperomys, Onyehomys, 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 dilTereut from 

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

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

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

 being found in the leucopus group, a species of which nuttalli, yellowish 

 underneath comes near Calomys. 



I propose to retain Hespei'omys 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. 



