FALCONIDiB — THE FALCONS. 221 



of the chord of the cuhnen, its upper outline greatly ascending basally ; commissure with 

 a prominent festoon. Superciliary shield very prominent. Nostril broadly ovate, 

 obliquely horizontal. Tarsus longer than the middle toe, the frontal and posterior series 

 of regular transverse scutelke very distinct, and continuous, sometimes fused into a con- 

 tinuous plate (as in the Turdince .'). Outer toe longer than the inner; claws strongly 

 curved, very acute. Wing short, much rounded, very concave beneatli ; third to fifth 

 quills longest; first usually shortest, never longer than the sixth; outer three to five with 

 inner webs cut (usually sinuated). Tail long, nearly equal to wing, usually rounded, 

 sometimes even, more rarely graduated {Astur macrourus) or emarginated (some species 

 of subgenus Xisus). 



Subgenera. 



Less than one third of the upper portion of the tarsus feathered in front, 

 the feathering widely separated behind ; frontal transverse scutellaj of the 

 tarsus and toes uninterrupted in the neighborhood of the digito-tarsal joint, 

 but continuous from knees to claws. Tarsal scutelliB sometimes fused into 

 a continuous plate ........... Xisns. 



More than one third (about one half J of the upper portion of the tarsus 

 feathered in front, the feathering scarcely separated behind ; frontal trans- 

 verse scutelte of the tarsus and toes interrupted in the region of the digito- 

 tarsal joint, where replaced by irregular small scales. Tarsal scutelhB never 

 fused Astur. 



The species of this genus are exceedingly numerous, about fifty-seven 

 being the number of nominal "species" recognized at the present date. 

 Among so many species, there is, of course, a great range of variation in the 

 details of form, so that many generic and subgeneric names have been pro- 

 posed and adopted to cover the several groups of species which agree in 

 certain peculiarities of external structure. That too many genera and sub- 

 genera have been recognized is my final conclusion, after critically examin- 

 ing and comparing forty of the fifty-seven species of Gray's catalogue (Hand 

 List of Birds, I, 1869, pp. 29-35). The variation of almost every character 

 ranges between great extremes ; but when all the species are compared, it is 

 found that, taking each character separately, they do not all correspond, and 

 cross and re-cross each other in the series in such a manner that it is almost 

 impossible to arrange the species into well-defined groups. From this genus 

 I exclude LopJiospiza, Kaup (type, Z. trivirgatus) ; Asturina, Vieill. (type, A. 

 nitida) ; Rupornis, Kaup (type, It. mcuinirostris) ; Buteola, Dubus ( = Buteo, 

 type, B. hrachijura, Yieill.) ; included by Gray under Astur, as subgenera, 

 and Tachys'piza, Kaup (type, T. soJoensis) ; and Scelospiza, Kaup (type, S. 

 fraiicesii) ; which are given by Gray as subgenera of Micronisus, Gray 

 (type, Accipitcr gdbar), the species of the typical subgenus of which, as 

 arranged in Gray's Hand List, I refer to Nisus. All these excluded names 

 I consider as representing distinct genera. 



The species of this genus are noted for their very predatoiy disposition, 

 exceeding the Falcons in their daring, and in the quickness of their assault 

 upon their prey, which consists chiefly of small birds. 



