FALCONID.E — THE FALCONS. 313 



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 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 too ; outer toe equal to, or longer than, the 

 inner ; claws very long and strong, very mucli graduated in size ; seutellaj of the toes 

 small except on the terminal joint, where they form l)road transverse plates; -tarsi densely 

 feathered all round down to the base of the toes; tibial plumes well developed, loose- 

 webbed, their ends reaching down to or lieyond 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 Nortli 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 Bidco to that of a sea-eagle (Haliaetns), 

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

 species. The species of Ifcferopus, Hodgson, 1842 {A. malayensis, Eein. and 

 H. f/urnci/i, Gray), I remove entirely from Aquila, since they differ so strik- 

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

 Hcterojms has the outer toe disproportionately shorter tlian the inner (in- 

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

 Gcranosinza of tropical America, and Polyhoroidcs of South Africa, — both 

 terrestrial Buteonine forms of specialized structin-e. An entirely peculiar 

 feature of Hetcroinis is the great length and straightness of the claws. Its 

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



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

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



Species and Races. 



A. chrysaettTS. Wiiip' 2:!.00 - 27.00 ; tail, U.OO - 16.00 ; culmen, 1.50- 

 l.'JO ; 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 

 Ijeneath the surface. Yomig. Tail with the basal half plain white, the ter- 

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

 the surface. Hah. Noarctic and Pal^arct.ic Realms. 



Tarsi of adult p.ale umber; of young, dirty whitish. H<ih. Patearctio 



Re.ilm \M-.chrysattH!:} 



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



Realm . . . . • . • • • \av. cav ad en sis. 



1 Af{iiila chrt/sae/n.% var. ckrij.mehis (Lixx.). Aquila Valeria, Alhin, B, II. pi. ii. Aquila 

 chi-ysaetus, Bkiss. Orn. I, 431, et Aucr. Falco dmjsaelus, Lixx. S. N. 1760, 125. Aquila 

 vol.. HI. 40 



