1873.] 79 [Ridgway. 



Sp. ch. Wing, 6.30-7.30; tail, 7.00-8.00; culmen, .50-65; tarsus, 

 2.20-2.35; middle toe, 1.10-1.25; graduation of tail, 1.50-2.00. (Ex- 

 tremes of 3 7 specimens.) Adult without any nuchal collar and with 

 the lower tail-coverts barred. Adult. \_a. Normal plumage.'] Abore 

 slate-color, sometimes more or less tinged with sepia, occasionally 

 quite rufescent on the wings. Tail darker, with 4-6 narrow, inter- 

 rupted bars of white. Head and neck, (all round), uniform ashy, 

 darker on the pileum, paler on the throat. Lower parts, and lining 

 of the wing, white, the whole surface about equally barred with dark 

 slate; pectoral region often more or less tinged with rufous. (=gil- 

 vicollis Vieill., and zonothorax Cabanus). [p. Rufescent plumage.'] 

 Above sepia-brown, with a rufescent cast, the pileum more grayish; 

 tail darker, with 4-6 narrow bars of whitish ; head, neck and breast 

 continuous brownish, the tint rufous on the breast, more grayish on 

 the pileum, and whitish on the throat. Lower parts white, with reg- 

 ular transverse bars of dusky, about equal to the white ones in width ; 

 crissum and lining of the wing similarly barred. (— ruficollis Vieill, 

 and xantliothorax Spix.) Young. Head, superiorly and laterally, 

 brownish black, the auriculars more brownish ; rest of the upper 

 parts dark sepia-brownish, separated from the blackish of the head 

 by a narrow, sometimes nearly concealed, nuchal collar of whitish; 

 longer scapulars and inner secondaries sometimes showing obscure 

 bars of lighter brownish, on either web. Tail as in the adult. Be- 

 neath, pale ochraceous, or ochraceous-white, the throat and anal- 

 region purer white ; breast, sides, and tibiae with more or less numer- 

 ous narrow transverse bars of dusky brown, much more distant, 

 sparse, and irregular than in the adult. (=: guerilla Cassin.) 



Specimens examined. Nat. Mus., 11 ; Philad. Acad., 9 ; N. Y. Mus., 

 1 ; Boston Soc, 9 ; Mus. Cambridge, 2 ; Cab. G. N. L., 5. Total, 37. 



Hab. Whole of Continental Tropical America, from eastern Mex- 

 ico (Jalapa) to southeastern Brazil and western Ecuador. The follow- 

 ing localities represented by the specimens examined : — Guatemala, 

 Costa Rica, Jalapa, Mexico, Guyaquil, Panama and Brazil. 



There can be no doubt that the rufescent plumage described above, 

 and identified as ruficollis of Vieillot and xantJiothorax of Spix, is a 

 phase of the same species as the grayish plumage to which the names 

 gilvicollis Vieillot and zonothorax Cabanis belong, as they are connected 

 by a gradual transition in intermediate specimens contained in a large 

 series. This is the sole instance, to our knowledge, among the Fal- 

 conidoz of a kind of dimorphism analogous to that seen in some owls, 



