BIRDS. 13 



an elevated hony tubercle in the centre. They were once considered to form three dis- 

 tinct genera, viz. — Milvago, Sjrix. (Polyborus, Vieill. Haliaetus, Cuv. Aquila, Meijen.) 

 — Senex, Gray. (Circaetus, Less.) — Phalcobaenus, D'Orh. but a careful com- 

 parison of the several species, shows a regular gradation in structure from 

 one to the other, which induces me to consider them as only forming two 

 sections of one genus. Those which have the bill short, with the culmen 

 arched, and are of small size, slender form, and with the tarsi rather long and 

 slender, are — 



1. Milvago ochrocephalus, Sjnx. 



Polyborus chimachima ; Vieill. (young). 

 Falco degener, Licht. 

 Haliaetus chimachima, Less. 



2. Milvago pezoporos, nob. 



Aquila pezopora, Meyen. 



3. Milvago chimango, n. 



Polyborus chimango, Vieill. 

 Haliaetus chimango, Less. 



Those which have a buteo-like appearance, and with rather short and stout 

 tarsi, are, 



7. Milvago leucurus, n. 



Falco leucurus, Forster's Drawings No. 34. 

 Falco Novae Zealandise, Gm. 



Australis, Lath. 



Circaetus antarcticus. Less. 



8. Milvago albogularis, n. 



Polyborus (Phalcobanus ?) albogularis, Gould. 



9. Milvago montanus, n. 



Phalcobaenus montanus, UOrVig. 



10. Milvago megalopterus, n. 



Aquila megaloptera, Meyen. 



1. Milvago pezoporos. 



Aquila pezopora, Meyen. Nov. Act. Phys. Med. Acad. Cees. Leo. Car. Nat. Cur. suppl. ISSJ'. p. 62. pi. VI. 



I obtained two specimens of this bird, one from Port Desire, in Pata- 

 gonia, and another at the extreme southern point of Tierra del Fuego. 

 Meyen* describes it as common on the plains of Chile, and on the mountains 

 to an elevation of 4000 or 5000 feet. As M. D'Orbigny does not notice this 

 species, I presume it is not found on the Atlantic side of the continent, so far 

 north as the Rio Negro, where he resided for some time. The habits and 

 general appearance of M. chimango and this bird are so entirely similar, that 



* Novorum Actorum Academise Caesarlee, Lcopol. vol. xvi. p. 62. Observationes Zoologicas, F. J. Meyenii. 



