FALCONIDyE — THE FALCONS. 107 



Subgenera. 



One primary only with inner \vi.'b emurginated ; lirst to second longest; 

 first longer tlian fourth. 



Tarsus longer than middle toe, and feathered Far below the knee ; first 

 quill shorter than third. Coloration of the sexes alike ; old and young 

 slightly diflferent in pattern and tints. Size large . . . Hierofnhn. 



Tarsus not longer than middle toe, and searcely leathered below the 

 knee ; first quill equal to or longer than the third. Coloration of the 

 sexes alike ; old and young very different in pattern and tints. Size, 



very small to large Falcn. 



Two primaries with inner webs emarginated ; seconil to third longest; 

 first shorter than fourth. 



Basal joint of toes without transverse scutelke; tarsus about equal to 



middle toe. 



Coloration of the sexes in adult plumage very difterent in 

 tints ; in the young alike, the young g resembling tlie .adult 



9. Size small JLxalnn. 



Basal joint of toes with transverse scutella; ; tarsus longer tlian mid- 

 dle toe. 



Coloration of the sexes very different, in pattern and tints, at all 

 ages ; old and young alike. Scutelte of the toes and tarsus inter- 

 rupted at the digito-tarsal joint ; tarsus much longer than middle 

 toe. Bill small, the cere on top less than one fouith the culmeu. 

 Size small .......... Tiunuitcuhis. 



Coloration of the sexes alike at all ages; old and young slightly 

 difierent in pattern and tints. Scutellfe of tarsus and toes uninter- 

 rupted from " knees " to claws ; tarsus but little longer than mid- 

 dle toe. Bill large, the cere on toj^ about one third the culmen. 

 Size medium; form very slender ..... Rhi/nrho/alco. 



Subgenus HIEROFALCO, Cuvier. 



Hierofalco, CnviEr., 1817. (Typ«> Fcdco gyrfako, Linn.) 

 Jerafalco, BoiE, 1822 ; Kaup, 1851. (Same type.) 

 Gcnnaia, Kaup, 1847. (Type, Faho jugrjer, Ghay.) 



Species and Races. 



1. F. gyrfalco. Wing, 13.00- 17.00 ; tail, 8.50- 11.50 ; culmon, .85- 1.05; tarsus, 2.10- 

 3.00 ; middle toe, 1.80 - 2.25.' Ground-color varying from entirely pure white to wholly 

 dusky, but generally bluish (in adult) or grayish-brown (in young) above, and white 

 beneath. Adult. All the markings transverse.^ No lighter nuchal band. Youncj. Mark- 

 ings of the lower surface longitudinal, the upper parts without transverse bars (except 

 on the tail'). 



a. Lower parts with white predominating, or wholly white. 



Lower tail-coverts never with marking.?. No tinge of blue anywhere on 

 the plumage, the ground-color of which is entirely pure white at all ages. 



1 Extremes of sixty .specimens. 



- Somutime.s thure are more or less distinct linear streaks on tlii' licad and neck, or on the 

 pectoral region. 



" Sometimes the iiTegular iiiarking.s above have a transverse tendency. 



