30 FALCONID^. 



Family FALCONIDtE. 



Crown of head alwa5's clothed with feathers, though the sides of 

 the face are often more or less bare. 



a. Both outer and inner toe connected to middle 



toe by basal interdigital membrane . . POLYBORINjE,^.&0. 

 h. Outer toe only connected to middle toe by in- 

 terdigital membrane. 

 a'. Tibia and tarsus to all intents equal in 

 length, the difference between them 



not so great as length of hind claw. ACCIPITRIN^,^AQ. 

 b'. Tibia much longer than tarsus, always 

 exceeding it by more than length of 

 hind claw. 



a". Hmder aspect of tarsus scaled BUTEONIN^, p. 158. 



i". Hinder aspect of tarsus reticulate. 

 a'". Commissiu;e of bill simply fes- 

 tooned AQUILINJE, p. 225. 



b'". Commissure of bill distinctly 



toothed ■. FALCONINjE, p. 350. 



Subfamily III. POLYBORIN^. 



All the toes connected near the base by interdigital membrane ; 

 sides of face for the most part bare. 



The members of this subfamily are chiefly American, and are 

 rather Gallinaceous in their habits, thus approaching the Turkey 

 Vultures, with which they are closely associated by Professor Sun- 

 devall (Av. Tent. pp. 109-111). Several subgenera are included 

 within the genus Ihycter, but are treated here as of subordinate 

 rank in the face of the instability of the characters and the gradual 

 gradation of one form towards another. The same idea was once 

 entertained by Dr. Kaup (Arch. f. Naturg. vol. xvii. 1850, p. 41) 

 before he had " given up subgenera, and had raised all subgenera 

 established by him to the dignity of genera" (P. Z. S. 1867, 

 p. 169). 



Key to the Genera. 



a. Middle tail-feathers not elongated. 



«'. Nostrils oval 11. Polyborus, p. 31. 



b'. Nostrils round 12. Ibycteb, p. 34. 



b. Middle tail-feathers extremely elongated ; 



head with elongated plumes. 

 n'. Nostrils vertical ovals ; forehead with 



erect crest 13. Oabiama, p. 42. 



b'. Nostrils perpendicular ovals; forehead 



not crested 14. Sehpentabius, p. 44. 



