104 NORTH AMERICAN BIRDS. 



B. Nasftl hones very incompletely ossified, the nostril l)eing a large, more or less 

 oval, opening, of ol)li(iue ilireetion, its lower end heing invariably the posterior 

 one ; without a bony tuljercle, and never perfectly circular. {Accipitrinae.) 

 a. Sides of the head densely feathered close up to the eyelids. 



.'). Pandion. Outer toe reversilile; claws contracted and rounded 

 on their tnider surliice, and not gradimted in size.' Wing Ion"-, 

 third quill lonjjust ; outer four with inner webs eniarginated. Tail 

 rather short, rounded. 



4. Naiiclerus. Outer toe not reversible; claws not contracted or 

 rounded on under side, and graduated in size. Wing louf. third 

 quill longest ; outer two with inn(n- webs sinuated. Tail excessively 

 lengthen(.'d and forked, the lateral |)air of feathers more than 

 twice as long as tht^ middle pair. 

 6. Sides of the- head with a more scantily feathered orbital space, with a 

 projecting .suitereiliary " shield " covered with a naked skin. 



* A well-developed membrane, or " web," between the outer and mid- 

 dle toes at the base. 

 t Tarsus about equal to the middle toe. 



§ Claws short and r()l)ust ; two outer quills with their inner webs cut. 

 ij. Ictinia. Commissure irregularly toothed and notched; front 

 of tarsus with transver.se .seutelhe. Tail eniarginated ; third quill 

 longest. 



G. Elanus. Commissure without irregularities ; front of tarsus 

 with minute roundish scales. Tail double-rounded : second quill 

 longest. 

 §§ Claws long and slender; five outer quills with iimer webs cut. 



7. RoBtrhamuB. End of bill bent downward, with a long pendent 

 hook ; inner edge of middle claw slightly pectinated, or .serrated. 

 Tail emarginated ; third or fourth quill longest. 



ft Tarsus very much longer than the midille toe. 



T Front of tarsus unfeathered, and, with the jiosterior face, covered 

 with a coiitiiuious .series of broad transver.se scutellse. 

 a. Form very long and .slender, the liead small, the tail and legs long and 

 claws excessively acute ; bill weak, compressed, very high through the 

 ba.se, the culmeii greatly ascending basally, and the cere much arched ; 

 commissure usually with a very prominent " festoon." 



8. Circus. Face surroimded by a " rulT" of stiffened, differently 

 formed feathers, as in the Owls. Taivsus more than twice as long 

 as the middle toe. Wing very long, hardly concave beneath; 

 third to fourth quill longest ; outer four with iimer webs siimated. 



9. NiBUB. Face not surrounded by a ruff. Tarsus less than 

 twice as long as the middle toe. Wing short, very concave 

 beneath, the outer quill much bowed ; third to fifth quills longest ; 

 outer five with imur w(,'bs sinuated. 



p. Form short and heavy, the head larger, tht; tail shorter, the legs more 

 robust. Bill stronger, less compressed, lower through the base, the 

 upper oTitlini! less ascending basally, and the cere less arched. Com- 

 missure variable. 



1 By this i,s inoaiit that they aro all of eiiuiil U'ngth and thiokness, and not progi-e.ssivoly 

 smaller from the po.stcrior one to the outer, lus in all Fakuitidw with the sole e.xeeptioii of I'andiun, 

 lliough there is a veiy near aiiproacli to this feature in one or two of the s])<'<'ic.s of ITnJia-fm. 



