MUUIDAE-SIOMOnONTES-nKSPEKOMYS. 



45 



an entirely diirerent genus. And although other species of tiie large genus 

 Hesperomys may not necessarily be separated generically, yet the subgenera 

 seem entirely different. The form Onjzomys appears not to be represented 

 at all in South America ; while, likewise, the form Oxymicterus of South 

 America has no exact analogue. Onychomys and Habrothrix would seem to 

 represent each other in their arvicoline form, yet they are abundantly worthy 

 of subgeneric separation. Probably the closest approach to identity of form 

 is found in the North American leucopus group (and especially tlie species 

 aureolus or nuttallii, where alone we have yellowness underneath) with the 

 Calomys group (i. e., Hesperomys sensu strictiss.) ; but even here there is 

 room for the subgeneric separation that we make in the succeeding article. 



In our comparative ignorance of the South American forms, we shall not 

 venture upon any diagnosis or description of the full genus Hesperomys. 

 Ample details of the North American forms will be found under the respect- 

 ive heads of Vesperimus, Onychomys, and Oryzomys. For similar reasons, we 

 refrain from any but North American citations in the foregoing list of 

 synonyms. ' • •; / 



We append a table, which may serve to exhibit the correspondences or 

 other relations of the North American with South American forms. 



North Ameeican. | South American. 



a. With groaced upper incisors. 



Genua Ociietodux, Cuiies. Furin niiiriue. | Geuus REmiKonoN, Waterli. Form leporine. 



b. With smooth upper itioisors. 



SubKenns Vkspkrimits, Cones. Form murine. 

 Subgeuua Onyciiumyh, Baird. Form arviuuline. 



f 



Snbgenna Oryzomys, Bairil. Form rat-liko. 

 Oeiiua HoLOCiiiLUK, Umiidt. Furui rut-like. 

 1 



Subgenus Calomys, Wnterb. Form murine. 

 Bnbgenus HAnROTiiRix, Waterh. Form arvicoline. 

 Subgenus OxYMictBHUs, Waterh. 



f 



Genna Sigmodon, Say. Form arvicoline. 

 Genua Nkotoma, Say. Form rat-li' e. 



Subgenus VESPERIMUS, Coues. 



= ifutculut, Rafikkkqur, Am. Monthly Hog. iii, IdlS, 44G (leumpiu). 



< Henperomyi, of North American writers. 



= Htupvromyii, Kaihd, M. N. A. 1H57, 4r)8 {leucoput). 



> Cttlomut, Ai;i>. & Bai;ii., Q. N. A. ii, IS51, 303 (onreo/m). Not of Waterbouse. 



= Ve»ptrimHt, C0UE8, 1'roo. Acad. Nut. Sci, I'bila. 1874, 178 (type, Mnt lencopHi, anc'.) 



We restrict our term Vesperimus to leucopus and its immediate North 

 American allies. As intimated in the foregoing article, it is exactly equivalent 



