BIRDS. 
13 
an elevated bony tubercle in the centre. They were once considered to form three dis- 
tinct genera, viz. — Milvago, (Polyborus, Vieill. Haliaetus, Cuv. Aquila, Meyen.) 
— Senex, Gray. (Circaetus, Less.) — Phalcobaenus, D'Orb. 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, Spix. 
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, Forsters Drawings No. 34. 
Falco Novee Zealandise, Gm. 
Australis, Lath. 
Circaetus antarcticus, Less. 
8. Milvago albogularis, n. 
Polyborus (Phalcobaenus ?) albogularis, Gould. 
9. Milvago montanus, n. 
Phalcobaenus montanus, D’Orhig. 
10. Milvago megalopterus, n. 
Aquila megaloptera, Meyen. 
1. Milvago pezoporos. 
Aquila pezopora, Meyen. Nov. Act. Phys. Med. Acad. Cass. Leo. Car. Nat. Cur. suppl. 1834. p. 62. pi. YI. 
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 Caesarise, Leopol. vol. xvi. p. 62. Observationes Zoologicas, F. J. Meyenii. 
