96 



BULLETIN 50, UNITED STATES NATIONAL MUSEPM. 



5-5.5 (5.1); width of bill at frontal antise, 4; tarsus, 10-11 (10.6); 

 middle toe, 9.5-11 (10.1)." 



Young. — Above ^lain sooty grayish brown, darker on back, where 

 faintly glossed with purple, violet, or bronze; a white patch on each 

 side of rump, as in adults; Idres dusky gray; auricular region and 

 postocular spot mottled sooty brown and grayish white, or uniformly 

 of the former color; under parts grayish white anteriorly, pure white 

 posteriorly, the chest usually tinged with sooty brown, especially 

 laterally, where sometimes vfith a distinct narrow transverse patch of 

 brown.* 



In winter plumage adults have the tertials conspicuously margined 

 with white. 



Western North America; north to Alaska (Yukon Valley, Fifty 

 Mile River, Fort Selkirk, Semenow Hills, etc.), east to Montana, 

 Wyoming, Colorado, New Mexico, and western Texas — occasionally 

 to South Dakota; breeding southward to southern Calif ornia^'^ Arizona, 

 and New Mexico; in winter south to highlands of Guatemala (Duenas; 

 San Geronimo; Coban; Hacienda Chancol), and Costa Rica (Matina 

 River, Atlantic side; Bebedero, Pacific side). 



Hirundo thalassina (not of Swainson) Ohnithologioal Committee, Journ. Ac. 

 Nat. Sci. Philad., vii, 1837, 193 (Columbia E.).— Audubon, Orn. Biogr., iv, 

 1838, 597, pi. 385, flgs. 4, 5; Synopsis, 1839, 36; Birds Am., oct. ed., i, 1840, 

 186, pi. 49. — Bonaparte, Geog. and Comp. List, 1838, 9, part. — Woodhouse, 

 Eep. Sitgreaves' Exp. Zuiii, etc., 1853, 64. — Cassin, lUustr. Birds Cal., Tex., 



« Ten specimens. 



Specimens from different parts of the country average in measurements as follows: 



^The young of this species considerably resembles that of Iridoprocne bicolor, but 

 may readily be distinguished by the grayish white instead of pure white throat, etc., 

 the white patch on each side of rump, and the much less abrupt definition of the 

 sooty color of the upper part of the head against the white below it. 



"Probably to northern Lower California (San Pedro Martir Mountains), but I 

 have not seen specimens from there. < 



