FALCONID^ — THE FALCONS. 313 



tions very deep. Tail rather short, shghtly rounded or wedge-sliaped. Bill stronger than 

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

 ward at the point; commissure with a more or less prominent festoon; nostril narrowly 

 oval, vertical; skin of the cere very hard and firm. Superciliary shield very prominent. 

 Feet very strong, the membrane between the outer and middle toes very well 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 ; scutellse 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 developed, loose- 

 webbed, their ends reacning down to or beyond the base of the toes. Feathers of the 

 nape and occiput lanceolate, acute, and distinct, forming a nuchal " 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 member 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 a Biiteo to that of a sea-eagle {Hcdiaetus), 

 the generic characters given in the above diagnosis apply well to all the 

 species. The species of Heteropus, Hodgson, 1842 (A. malayensis, Rein, and 

 H. gurneyi, Gray), I remove entirely from Aquila, since they differ so strik- 

 ingly in many important respects. With the general aspect of Aquila, 

 HetcTopiis has the outer toe disproportionately shorter than the inner (in- 

 stead of equal to it, or longer), wliich curious feature it shares only with 

 Geranos'piza of tropical America, and Polyhoroides of South Africa, — both 

 terrestrial Butconine forms of specialized structure. An entirely peculiar 

 feature of Hdero-pus is the great length and straightness of the claws. Its 

 bill is more like that of Archihuteo than like that of Aquila. 



The North American and European races of the single species which oc- 

 curs on the former continent may be distinguished as follows: — 



Species and Races. 



A. chrysaetus. Wing, 23.00-27.00; tail. 14.00-16.00; culmen, 1.50- 

 1.90 ; tarsus, 3.40 - 4.20 ; middle toe, 2.40 - 3.10. Third to fifth quill longest 

 first shorter than seventh or eighth. Color blackish-brown, or umber-brown, 

 nearly uniform, except on the tail ; nuchal cape of lanceolate feathers, and 

 tarsi of a paler and more tawny tint. Adult. Tail transversely clouded with 

 ashy, and not white at the base; feathers of the body not distinctly white 

 beneath the surface. Young. Tail with the basal half plain white, the ter- 

 minal portion plain blackish ; feathers of the body distinctly white beneath 

 the surface. Hah. Nearctic and Palaearctic Realms. 



Tarsi of adult pale umber ; of young, dirty whitish. Hah. Paltearctic 

 Realm .......... var. chrysaetus.^ 



Tarsi of adult deep umber; of young light brown. Hah. Nearctic 

 Realm .......... var. canadensis. 



^ Aquila chrysaetus, var. chrysaetus (Linn.). Aquila Valeria., Albin, B, II. pi. ii. Aquila 

 chi-ysaetiis, Briss. Oru. I, 431, et Auct. Falco chrysaetus, Linn. S. N. 1760, 125. Aquila 

 VOL. III. -iO 



