irst upper incisors inscribing
an arch of a circle the radius of which is more than 9.6 mm.

5. Geographic range east of Mackenzie River.
_Lepus arcticus_, p. 178

5'. Geographic range west of Mackenzie River.
_Lepus othus_, p. 177

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