178 PROCEEDINOS OF THE NATIONAL MUSEUM. vol. xxvii. 



This dichromatism, or rather, polychroniatisin, together with ))etter 

 knowledge of actual distribution, serve to explain awa}^ the supposed 

 interrupted distribution of one or two West American races. 



In the present investigation the author has been much aided hy the 

 collection of the Biological Survey, by access to the collection of thelJ. S. 

 National Museum that Mr. Ridgway has accorded, and by the loan of 

 specimens from Mr. William Brewster, Mr. Outram Bangs, Dr. Louis 

 B. Bishop, Mr. Jewell D. Sornborger, and the Academy of Natural 

 Sciences of Philadelphia through Mr. Witmer Stone. 



ANALYTICAL KEY TO THE AMERICAN FORMS OF ASIO, BASED ON 



ADULT FEMALES. 



I. Wing averaging less than 350 mm. 



A. Wing averaging less than 320 mm. 



a. Exiiosed culmen less than 40 mm dacJnstus. 



a ^. Exposed culmen not less than 40 mm niayensis. 



B. Wing averaging more than 320 mm. 



(f. More rufescent throughout mefcmhrlnus. 



a^. Less rufescent throughout. 



J). Upper parts darker vigrei<cens. 



h'^. Up2)er parts lighter. 



c. More finely barred below; bill smaller vKigdhtnicus. 



r'. More coarsely barred below; bill larger niekuicents. 



II. AVing averaging more than 350 mm. 



A. Wing averaging over 370 mm. 

 (I. Light colored. 



b. Very pale; feet immaculate vitpiwiifJttt. 



b^. Darker; feet more or less spotted. 



c. Darker above; lower parts more heavily l)arred nhjifttiis. 



r\ Lighter above; lower parts less heavily barred occidentaVis. 



«\ Dark colored. 



b. Face and notanim more blackisli, less rufescent. 



c. Lower parts paler; feet less mottled hderncnemis. 



r\ Lower parts darker; feet more heavily mottled aaturatus. 



b^. Face and nota^um lighter, more rufescent Jagophomis. 



B. Wing averaging xmder 370 mm. 

 It. U})per i^arts lighter. 



/'. Face and lower jjarts lighter; feet less spotted palk'ticms. 



Ii ^ Face and lower parts darker; feet more spotted ]>arijiciis. 



(1^. Vpper parts darker. 



b. Wing averaging over 360 mm. ; very rufescent virghiUimn^. 



b\ Wing averaging under 360 mm. ; less rufescent. 



c. More blackish above; feet scarcely mottled ■iiigreHcens. 



("\ Less blackish above; feet much mottled Icelus. 



ASIO MAGELLANICUS MAGELLANICUS (Gmelin). 



StrLv bubo d. magellunicus Gmelin, Syst. Nat., I, 1788, p. 286. 

 Strix nacurutu Vieillot, Nouv. Diet. d'Hist. Nat., YII, 1817, p. 44. 



Type locality. — Southern South America. 



Geograjylncal dhtrihntion. — Southern South America, north to Peru 

 and Southern Brazil. 



