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44 



MONOGUAITIS OK NORTH AMEllICAN KODENTIA. 



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iiig his comparisons between Miis ivnd the new groui) he was about to estab- 

 lish, he liappcncd to select Mu.s rattus and Mus hlmaiulatus for that purpose. 

 We may therefore, with entire propriety, elect Mm himaculatus as technically 

 the type of Hcyirivmi/s. When, in 1837, Waterlunisc established the sub- 

 genus Calomi/s upon C. ekgans, he included in it both bimacutatus and graci- 

 llpn. Eligmodontia of F. Cuvicr, of tlu; same date, has the same strictly 

 consul)gencric species as its type. It is a cpiesfion, therefore, whether either 

 Cdliiiiujs or Eligmodontla ought not to take precedenc^c over Hesperomys ; but 

 as the latter name has become firmly established, and as the prior name 

 Cdloinys is by the same author, and at least as early as Eligmodontui, there is 

 really no necessity for a change. 



Resting, then, upon this application i)i Hesperomys, in its strictest subgen- 

 "ric sense, to such species as biiiiaciilatu.s, elegmis, and gracilipcs, we will inquire 

 how far th(! name may l)e extended in its generic application. In his able 

 e.ssay of 1857, Professor Baird points out, in elaborate detail, the characters 

 of the South American species, and, excluding ReUhrodon and Holocheilus as 

 worthy of full generic rank, he makes Hesperomys to include three subgenera, 

 \'h.,—C(i/omys, Waterh. ; Hahrothrix { = H<ihrolhrix plus P/iyllotis, Waterh.) ; 

 and Dxymiclrrus { — Oxymklcrus jdus Scnpleromys, Waterh.). Recurring to 

 the North American forms, he establishes three subdivisions, — Hesperomys, 

 Onychomys, and Oryzomys* We arc able to confirm the validity of these 

 groups in the most unequivocal manner ; the only question being whether 

 the leucopus group tn. t Professor Baird left in the subgenus Hesperomys is 

 not entitled to subgeneric distinction from the South American himaculatus. 

 Prol'essor Baird himself suggests that this ought to be done ; and, so far os wc 

 can judge from the descriptions of authors, the suggestion is available. 



The Vesper mice of North America, collectively, seem to be difl'crcntiated 

 from those of South America by characters only less important than that one 

 which irenchantly divides them l)oth from Old World Mures. Neotoma of 

 North America has nothing whatever to correspond in South America. 1 e 

 large, leporine, grooved-incisor species of South America are generically differ- 

 ent from the little murine species that have been called ReUhrodon in North 

 America. Holuchilus has no nearer representative than Sigmodon, which is 



* Kcally lour Nuli(livi»i(in8, lu lin (liNtiiiKniHln's tlio niikcdfimlcil HpccicH (ta(i/onii<K« und rrtmic»$) 

 fiimi thii kiuoima tjiii'i Imt bo very iiri>)pi'rly rcfiiiiiis from Hauling thiH wclioii. It d(MW not n)ipear 

 to UN to 1111VUI.VUU biiligi'ucric value, iiu (lie b:iref»utedue»a is niercly au accideut of the uuiiunl's desert 

 liitbitul. 



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