PETROCHELIDON. 281 



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. H. nigricans, Yieill. ( Collocalia 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 

 Atticora and other genera. 



The diagnostic characters of the principal American species of 

 Petrochelidon are as follows : — 



Common Characters. — 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 . . . 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 . pceciloma. 



Chin, throat, and sides of head white. 



Fore part of breast chestnut, without black spot. 

 Sides faintly tinged with same. 

 Frontal band obsolete ..... rujicolhiris. 



P. nigricans, of Australia, lacks the nuchal band ; the sides of 



