126 
NORTH AMERICAN BIRDS. 
with inner webs cut. Tail rounded or cuneate, sometimes con- 
sisting of fourteen feathers. Iris brown in young, yellow in adult. 
Eggs always (?) white and unspotted in American species, the 
nest nearly always on trees. (Page 140.) 
™ Subfamily PALCONIM. c; 
EC1 
“ Genus FALCO, Auct. (Page 123.) “ 
a. Only one primary 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 alike ; old and young 
slightly different in pattern and tints. Size large. (Page 126.) . 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. (Page 128.) Falco. 
b. Two primaries with inner webs emarginated; second to third longest; 
first shorter than fourth. 
Basal joint of toes without transverse scutellae ; 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. (Page 129.) JEsalon. 
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. Scutellae 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. (Page .) . Tinnunculus. 
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. (Page .) . . Rhynchofalco. 
Subgenus HIEROFALCO, Cuvier. (Page 126.) 
1. F. 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. Young. 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 markings. No tinge of blue anywhere on 
the plumage, the ground-color of which is entirely pure white at all ages. 
1. Adult. Upper parts, excepting head and neck, with transverse 
crescentic bars of dark plumbeous; lower parts immaculate, or 
