The American Voles of fhc Gcmis Evotomys. 123 



to blai'k spot at liase of imistaclie. Smnmcr pelage : darker all over, with 

 more dnsk}' on feet and tail. Youiig : when half grown, similar to adults, 

 but with thinner surface colors, tlirouirh which the slaty under fur shows. 



Crduhd clKtracters. — Skull small and slender, not ridged or angular, ex- 

 cept in very old individuals; audital bullae small, full, and rounded, less 

 angular, elongated, and appressed than in carolinensis ; palate straight 

 edged, or rarely with a slight central projection ; molar row slender. 



Measurement.^. — Average of 4 adults assumed to be typical from Locust 

 Grove, N. Y., measured by Di-. C. Hart Merriam : total length., Ul ; tail 

 vertebrcie, 37 ; hind foot, 18.1. Average of 10 adults from Elizabelhtown, 

 N. Y., measured by Gerrit S. Miller, Jr.: total length, 141; tail verte- 

 bra?, 39; hind foot, 18.3. Average of 10 adults from Peterboro, N. Y. : 

 145; 40; 18.3. Skull from Emsdale, Ontario, Canada, old J*, No. 75896: 

 basal length, 21.6; nasals, 6.5; zygomatic breadth, 13.3 ; mastoid breadth, 

 11.2; length of upper molar series, 5. 



Bemarh. — Erofomys gapperi, with the possible exception of E. nitihi.i, 

 occupies the largest area of any species in America, and, as might be ex- 

 pected, presents considerable variation in the extremes of its range. Some 

 of the peripheral forms have become sufficiently marked to l)e worthy of 

 recognition by name, while others are barely distinguishable from the 

 central form. A decrease in size takes place in the prairie coiuitry of 

 JMinnesota and the Dakotas ; an increase beyond the normal in the north- 

 ern Rocky Mountains. North and east of the type locality another in- 

 crease is noticeable, especially in the feet. Specimens from Godbout, 

 Quebec, are larger even than ochraceous, though in color they appear to 

 be darker instead of lighter than gapperi ; ])ut they have been preserved 

 in wood alcohol, which has doubtless changed the color. 



Another peculiarity of the nortlieastern animal as it enters the Hud- 

 son ian zone is a tendency to dichromatism. Dr. .Alien first made known 

 the al>normal phase from Trousers Lake, New Brunswick, but supposing 

 it characterized a new s])ecies gave it the name fu.scodrjrsulis.* Normal, 

 and what were considered typical, gapperi were secured at the same place 

 and at the same time as the others. During the past summer Mr. Gerrit 

 S. jNIiller, Jr., collected series of specimens in both the gray and the red 

 pelages at Nepigon and Peninsula on the extreme north shore of Lake 

 Superior, which he has kindly placed at my disposal. In a critical com- 

 parison of measurements, skulls, and external characters of the two forms 

 I find no difference other than color, and am compelled to agree with the 

 previous conclusions of Mr. Miller f that tlie gray animal represents only 

 a color phase. 



The gray form is characterized by the entire absence of a rufous dorsal 

 stripe, in place of which there is usual! v a sooty or black stripe ; by clear 

 gray sides and light gray wash of tielly, and in very dark specimens by 

 clear Ijlack upper surface of tail. 



*Bull. Am. Mus. Nat. Hist., vol. VI, 103, 1894. 



t Notes on the Mammals of Ontario, by Gerrit S. Miller, Jr. Proc. 

 Bost. Soc. Nat. Hist., vol. 28, p. 16, April, 1897. 



