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MONOORAPIIH OF NOKTH AMEUIOAN KODBNTIA. 



IIESPFROMYS (VESPERIMUS) MICHIGANENSIS (A. & B.) Wngn. 



MIrblean Moune. 



Vim iiii(»ijiiii.n»i», Ann. & Bach., .Iiiiirn. Acad. Nut. 8ci. I'lillii. viil, il, \Mi, :)04i Q. N. A. Hi, 1854, 320. 

 llfpiromtjii micliiijanrmiii, Wac.nkh, \Vu'({. Arcliiv, 1843, il, fil.— lUlltn, M. N. A. lHf)7, 476. 

 IliKjiiiiimijii ( l'(»piT/;iiu») michiganeutii, CouKS, I'roc. Acjul. Nat. Si'l. I'lillo. 1874, 180. 

 MuH bnirdii, Hoy & Kknnicott, U. 8. raU-nt-Offlce Kcp. Agrlc. for IMWJ (18{)7), Oi, iil. xi. 



DiAONoaw. — //. minimus, (2J-3-j>o//.) auricuUs parvLs, ]>edibns breoibux 

 ij_M /)«// \ caudii truncum sine cnpite suhaquanle {\'^-l-poll.)^ supra cum pedi- 

 bus ,'iuiijulns((nli /irunnt'u.i, j'loi^a dorsali ob.scurioic ; infra cttudidus. 



Very hiiiiiII iiihiisv, ^cllipwi.sli-lirosvii above, with n broad dorsal stripe ol' 

 s(iot}-bro\vii, below ^nnv white; feet not entirely white, us usual in leucopus; 

 tail bicolor. IJurely 3 inches or mtire long ; hind foot never exceeding O.Tij, 

 oih-ii inut'li shorter; ears J, or less, high; tail about equal to the trunk 

 without the heatl. 



HAitiTAT. — Upper Mississippi Valley ; especially Illinois, Michigan, and 

 Wisconsin. Kansas. 



Without speculating upon the probable derivation by actual descent of 

 this species from 11. leucopus, we will rest upon the fact that here we have 

 un animal positively distinct from leucopus. The difTcrentiation from a com- 

 mon stock has proceeded so far that the connecting links, if any once existed, 

 arc broken or at least concealed. Out of a considerable number of speci- 

 mens (sec tal)le below), there is not a single one that is not disfinguislin'de 

 on sight fiom leucopus This, if not more remarkable, is, at any rate, the nioie 

 interesting and instructive, since the true leucojms abundantly inhabits the 

 regions where michiganensis occurs. As far as is known at present, mkhiga- 

 ncnsis is one of the most restrictedof our species in geographical distribution, 

 being nearly confined to the valley of the Upper Mississippi. This, probably. Is 

 the reason why it adheres so faithfully to one particular style ; and siiould it ever 

 become dispeised over an area large enough to bring difi'erent individuals 

 under decidedly ditferent climatic and other inlluences, a divergence and varia- 

 tion would undoubtedly ensue. The only sign of such possible or probable 

 ditfenMitiation at present is represented by what has been called Mus '"bairdii" 

 by Hoy and Kenuicott. These excellent naturalists were unquestionably 

 wrong in supposing a distinction of species here. Dr. Hoy ex|)ressed the 

 whole thing in a nutshell when he wrote to Professor Baird : — "One thing is 

 certain — we iind one species in the oak o|)enings, while the other is confined 



Ms" 



