482 BIRDS OF ILLINOIS. 



ance of these, however, on secondaries; rump entirely blackish brown; upper tail- 

 coverts wholly white. Tail hoary slate, basal third (or more) white, the junction of the 

 two colors irregular and broken; tip obscurely paler; feathers obscurely blackish along 

 edges, and with obsolete transverse spots of the same; white prevailing on inner webs. 

 Beneath entirely pure white, scarcely variegated; tibiae and tarsi with a few scattered 

 small transverse spots of blackish; flanks with larger, more cordate spots of the same. 

 (Breeds in this plumage.) 



This magnificent hawk, which Dr. Coues justly styles the "hand- 

 somest of the North American Falconidae," is perhaps little more 

 than a straggler to Illinois. It has been seen by the writer only in 

 the far West, where the few observed were sailing majestically over- 

 head, describing broad circles, and resembling the Golden Eagle in 

 the manner of their flight. At such times it may be immediately 

 distinguished from A. sancti-johannis by the snowy white of its 

 lower plumage, which, as seen from below, is the predominating 

 color of the bird. 



GENUS AQUILA BRISSON. 



A qyXla BBISS. Orn. 1, 1760. 419. Typo (by elimination). Falco ehrysaitos Lm. 



GEN. CHAE. Form robust and structure powerful; bearing and general aspect of 

 Buteo and Archibuteo. Wing long, the primaries long and strong, with their emarp' na- 

 tions very deep. Tail rather short, slightly rounded or wedge-shaped. Bill stronger 

 than in the preceding genera, its outlines nearly parallel, and the tip somewhat inclined 

 backward at the point; commissure with a more or less prominent festoon; nostril nar- 

 rowly oval, vertical; skin of the cere very hard and firm. Superciliary shield very prom- 

 inent Feet very strong, the membrane between the outer and middle toes very much 

 developed; tarsus less than twice as long as the middle toe; outer toe equal to, or longer 

 than the inner; claws very long and strong, very much graduated in size; scutellae of 

 the toes small except on the terminal joint, where they form broad transverse plates; 

 tarsi densely feathered all round down to the base of the toes; tibial plumes well devel- 

 oped, loose-webbed, their ends reaching down to or beyond the base of the toes. 

 Feathers of hind neck and occiput lanceolate, acute, and distinct, forming a "cape" of 

 differently formed feathers. Third to fifth quill longest ; first shorter than the seventh ; 

 outer five or six with their inner webs deeply emarginated. 



This genus is almost peculiar to the Old World, where about 

 seventeen so-called species are known, while America has no mem- 

 ber of the genus exclusively its own, the single North American 

 species being the same as the European one. Though the details 

 of external structure vary somewhat, and the size ranges from that 

 of Buteo latissimus to that of a sea-eagle (Haliceetus), the generic 

 characters given in the above diagnosis apply equally well to all 

 the species. 



