PETROCHELIDON. 287 
bases of the inner and middle toes. The lateral toes are nearly 
equal, the outer, if anything, slightly longer; the entire basal joint 
of the outer adherent to middle; the membrane just referred to ex- 
tending along the basal joint of the inner. The basal joint of the 
middle is free externally at extreme end. The feathers of crissum are 
very full, and reach nearly to end of tail. 
This is one of the most natural genera of American Swallows, em- 
bracing a considerable number of species, all characterized by the 
rufous rump. AH. nigricans, Vieill. ( Coilocalia arborea of Gould), 
from Australia, appears to be strictly congeneric, as first suggested 
by Cabanis. The development of bristles in the chin and among 
the frontal feathers appears quite characteristic, giving a roughness 
to the forehead very different from the softness and smoothness of 
Aiticora and other genera. 
The diagnostic characters of the principal American species of 
Petrochelidon are as follows :— 
Common Cuaracters.—Above steel blue; the feathers of the inter- 
scapulum with concealed whitish edges; no whitish median 
or basal down. Rump and narrow nuchal band chestnut; 
crissum gray brown, tinged anteriorly at least with chestnut ; 
the longer feathers and inner side of lateral tail feathers edged 
with whitish. Middle region of belly white. Usually with 
a whitish or reddish frontal band. 
Chin and throat, with side of head, and continuous with 
nuchal band, chestnut brown. 
Jugulum with large blue-black patch. Chestnut of 
throat darker than that of rump. 
Frontlet reddish-white, with narrow band of 
black along upper mandible . 0 . lunifrons. 
Frontlet chestnut brown, without black at 
base of upper mandible : - swainsoni. 
Jugulum plain, without black spot. Chestnut of 
throat lighter than that of rump.  Frontlet 
chestnut brown. 
Sides of body only slightly tinged with chest- 
nut - : : < : - fulva 
Sides deep chestnut, continuous with that of 
breast and crissum. Size smaller - peciloma. 
Chin, throat, and sides of head white. 
Fore part of breast chestnut, without black spot. 
Sides faintly tinged with same. 
Frontal band obsolete . - . : - ruficollaris. 
P. nigricans, of Australia, lacks the nuchal band; the sides of 
