Sonoran are the chipmunks (_Tamias_), beavers (_Castor_), meadow-mice (_Microtus_), the Muskrat (_Fiber zibethicus_). The white-footed mice (_Sitomys_) and the wood-rats (_Neotoma_) are southern rodents that reach or enter the Boreal. Between the Boreal subregion and the Sonoran region is the Transition zone, which follows all the complex windings of the boundary lines. It covers most of New England, New York, Pennsylvania and southern Ontario; passing through southern Michigan and Wisconsin, it bends northward over Minnesota and covers most of North Dakota, Manitoba and the plains of the Saskatchewan, then turns abruptly southward and includes eastern Montana and parts of South Dakota and Nebraska. Crossing Wyoming, it follows around the northern edge of the Great Basin to the plains of the Columbia. The three great mountain-systems carry the zone far to the south and arms of it extend along the Appalachians to northern Georgia, along the Rockies to New Mexico, and it follows the Sierras to southern California. “The Transition zone, as its name indicates, is a zone of overlapping Boreal and Sonoran types. Many Boreal genera and species here reach the extreme southern limits of their distribution and many Sonoran genera and species their northern limits. But a single mammalian genus (_Synaptomys_) [one of the field mice] is restricted to the Transition zone.... A number of species, however, seem to be nearly or quite confined to this zone” (Merriam). [Illustration: FIG. 61.—Upper figure, European Bison (_Bison bonasus_). Lower figure, American Bison (_B. bison_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 62.—Wolverene (_Gulo luscus_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 63.—Wapiti or “Elk” (_Cervus canadensis_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 64.—Alaska Brown Bear (_Ursus middendorfi_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 65.—Moose (_Alce americanus_). Young male with undeveloped antlers.—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 66.—Beaver (_Castor canadensis_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 67.—Woodland Caribou (_Rangifer caribou_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 68.—Red Fox (_Vulpus fulvus_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 69.—Rocky Mountain “Goat” (_Oreamnos montanus_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 70.—Ermine (_Mustela erminea_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 71.—Timber or Grey Wolf (_Canis nubilis_).—By permission of the N.Y. Zoölog. Soc.] [Illustration: FIG. 72.—Boreal Mammals. _A._ Black-footed Ferret (_Mustela nigripes_). _B._ Otter (_Lutra canadensis_). _C._ Jumping Mouse (_Zapus hudsonius_).—_A_ and _B_ by permission of the N.Y. Zoölog. Soc. _C_, by permission of W. S. Berridge, London.]