FALCONID^ — THE FALCONS. 107 



Subgenera. 



One primary only with inner web emarginated ; first to second longest ; 



first longer than fourth. 



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



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



slightly different in pattern and tints. Size large . . . Hierofalco- 



Tarsus not longer than middle toe, and scarcely feathered 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 .......... Falco. 



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



first shorter than fourth. 



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



middle toe. 



Coloration of the sexes in adult plumage very different in 



tints ; in the young alike, the young ^ resembling the adult 



9 . Size small ^salon. 



Basal joint of toes with transverse scutellae ; tarsus longer than 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 fourth the culmen. 

 Size small . . . . . . ■ . . . . Tmnuncuhis. 



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

 different in pattern and tints. Scutellae of tarsus and toes uninter- 

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

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

 Size medium ; form very slender ..... Rhynchofalco. 



Subgenus HIEROFALCO, Cuvier. 



Hierofalco, Cuvier, 1817. (Type, Falco gyrfalco, Linn.) 

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

 Gennaia, Kaup, 1847. (Type, Falco juggcr, Gray.) 



Species and Races. 



1. r. gyrfalco. Wing, 13.00-17.00; tail, 8.50-11.50; culmen, .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. Younq. Mark- 

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

 on the taiP). 



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



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

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



^ Extremes of sixty specimens. 



'^ Sometimes there are more or less distinct linear streaks on the head and neck, or on the 

 pectoral region. 



3 Sometimes the irregular markings above have a transverse tendency. 



