4´. Basilar length of skull less than 67; ear from notch usually less than 73 dry (77 fresh); first upper incisors inscribing an arch of a circle the radius of which is less than 9.6 mm. _Lepus americanus_, p. 173 3´. South of a line from Port Simpson, British Columbia to Halifax, Nova Scotia. 5. Ear from notch more than 82 dry (87 fresh); least interorbital breadth more than 26 _Lepus townsendii_, p. 180 5´. Ear from notch less than 82 dry (87 fresh); least interorbital breadth less than 26 _Lepus americanus_, p. 173 2´. Brownish or grayish pelage. 6. Tail blackish or brownish all around (in specimens not having completed molt on tail, white winter pelage may be present); basilar length less than 67 mm. _Lepus americanus_, p. 173 6´. Tail partly or wholly white. 7. Tail black on upper surface. 8. Upper sides of hind feet without a trace of white; upper parts tawny. _Lepus europaeus_, p. 189 8´. Upper sides of hind feet with more or less white or whitish; upper parts grayish or brownish _Lepus californicus_, p. 181 7´. Tail all white or (in some _Lepus townsendii_) with faint buffy or dusky median line on top but this line not extending on to rump (as in _L. californicus_). 9. Geographic range north of a line from Port Simpson, British Columbia, to Halifax, Nova Scotia. 10. Geographic range east of Mackenzie River _Lepus arcticus_, p. 178 10´. Geographic range west of Mackenzie River _Lepus othus_, p. 177 9´. Geographic range south of a line from Port Simpson, British Columbia, to Halifax, Nova Scotia _Lepus townsendii_, p. 180 1´. South of 34° N latitude. 11. In state of Tamaulipas, México. _Lepus californicus_, p. 181 11´. Range outside Tamaulipas, México. 12. Ears with terminal black patch (on outside). _Lepus californicus_ and _Lepus insularis_, pp. 181, 186 12´. Ears without terminal black patch.