3. _Adult._ Top of the head streaked with whitish; back with sharply defined, continuous, narrow transverse bars, of creamy-white. _Hab._ Interior regions of Continental Arctic America (Slave Lake, Yukon, and McKenzie River district) … var. _sacer_. 4. _Adult._ Top of head not streaked with whitish; back without sharply defined bars of the same. _Hab._ Continental Arctic Europe (Scandinavia) and Siberia. Migrating south, in winter, to Bengal (Hardwicke) … var. _gyrfalco_.[48] _b._ Lower parts with dusky predominating, or wholly dusky. 5. _Adult._ Almost entirely dusky, without well-defined markings anywhere. _Hab._ Littoral regions of the Hudson Bay Territory and Labrador … var. _labradora_. =2.= =F. lanarius.= Wing, 11.50–16.00; tail, 6.60–9.50; culmen, .70–1.00; tarsus, 1.90–2.40; middle toe, 1.65–2.00. Ground-color varying from pale grayish-plumbeous to dark sepia-brown; beneath white, with sparse markings, these coalesced into a broken patch on the flanks. _Adult._ Above obscurely barred transversely with pale ashy and brownish-dusky, the former prevailing posteriorly, the latter anteriorly; a lighter nuchal band. Spots on the sides and flanks transverse. _Young._ Above brown, varying from grayish-drab to dark sepia, the feathers usually bordered with paler (rusty in youngest individuals); markings beneath all longitudinal. _a._ Outer webs of tail-feathers with large well-defined light spots; outer webs of the primaries sometimes with light spots on the basal portion; secondaries without distinct spots on the outer webs. Lower tail-coverts immaculate. Wing, 13.65–16.00; tail, 8.40–9.50; culmen, .85–1.00; tarsus, 1.95–2.15; middle toe, 1.85–1.95. Top of the head white, with narrow streaks of dark brown. _Hab._ Central and Eastern Europe, Western Asia, and adjoining portions of Africa … var. _lanarius_.[49] _b._ Outer webs of tail-feathers without distinct light spots, or without any at all; outer webs of primaries with no trace of spots; secondaries with light spots on outer webs. Lower tail-coverts sparsely spotted. Wing, 12.00–14.25; tail, 7.60–9.00; culmen, .75–.90; tarsus, 2.15–2.40; middle toe, 1.70–2.00. Top of head brown, with narrow black streaks. _Adult._ Above with obscure transverse spots of bluish. _Young._ Above with feathers bordered with rusty … var. _polyagrus_.