722 



MUNUOItAPUS OF NOIITII AMKUICAN IIODKNTIA. 



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truxtwurtli}' c-lianicter ol' while iiuho und cars in vnr. niger, tliHugli opni t<i 

 many cxc(*|itiuiiH, is tliu one nmini}' to Ix; relied npon in distinguiBliinfj iho 

 two varieties. 'I'liere is a|ipareiitly n gradual and qnile marked incre»8e in 

 8i7.(> southward in tlii'se two forms, so that size alone fails to he distinctive, 

 espetnally in llu; central portion of the Atlantic Stat >8, or wherever their 

 iiiiltitats meet. 



Var. liidoricianux is generally readily separahic hy its coloration from 

 either var. cinereun or var. n'lgfr. The riisty-hellicd style of var. cinereua, 

 however, is often <|uite insi^parahle from specimens of vur. lu<iovicianu.t from 

 northern l()caliti(;s. Particularly is this the case when Pennsylvania speci- 

 mens of the riitous type are cinnpared with Qhio examples of var. ludovici- 

 aiiu.s. There are, for instance, two specimens hefore me without labels, an<l 

 hence from unknown localities, which I cannot positively refer to one of these 

 vari(!ties rather than to the other. Tlicre is little, if any, difference in size 

 between vars. cinereux and ludovicianus, altltough the latter is pretty constantly 

 npprecial)ly smaller than var. niger, as shown by a comparison of the forego- 

 ing diagnoses of the thn;e varietieu. 'Y\\q external measurements arc, unfor- 

 tunately, nearly all from skins, and are hence not very trustworthy. Taking 

 the skulls as a standard of comiuirison, var. niger averages appreciai)ly the 

 larger, four skulls of niger averaging 2.75 against 2.58 in both vars. lutlovici- 

 anus (eigiit skulls) and cinereus (three skulls). 



Oeookaimiical vauiation. — In varieties cinereus and niger, the only 

 a]»preciable feature of geographical variation is the before-noted gradual 

 increiisc in size southward. A large series of specimens, from numerous 

 localities, might show that other variations correlate with differences of 

 locality. My material illustrative of these two forms is unsatisfactorily 

 scanty. Var. ludovicianus, on the other hand (thanks to more abundant 

 material), shows strongly marked geographical variations in color, but I fail 

 to notice any well-marked geographical variation in size. Judging from the 

 skulls, the northern specimens are rather the larger, yet the largest skull of 

 the series is from Brookhaven, Miss. The measurements taken from tho 

 skins show also a rather greater size northward, the largest specimens 

 l)eing from Ohio and Fort Randall, Dakota, if length of l>ody be taken 

 as the standard ; if, on the other hand, the length of the hind foot be 

 adopted, in consequence of being less susceptible to variatiou resulting from 

 ta.\idcrmy, the southern specimens average nearly or quite as large as the 



