12 
ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
form like the P. Brasiliensis, mingled with the other carrion-feeding hawks on the 
banks of the Plata ; and there is now in the British Museum a specimen, which 
may be considered as partly an albino. Spix, on the other hand, (Avium Species 
Novae, p. 3.) has described some specimens from the coast of Brazil, as being 
remarkable from the darkness of the plumage of their wings. 
Milvago, Spix. 
Several new genera have lately been established to receive certain species 
of the sub-family of Polyborince, and consequently great confusion exists in 
their arrangement. Mr. George R. Gray has been kind enough to give me the 
following observations, by which it appears he has clearly made out, that Spix’s 
genus Milvago, is that which ought to be retained. M. D’Orbigny has made 
two sections in the genus Polyborus, according as the craw is covered with 
feathers, or is naked, and he states that the P. Brasiliensis is the only species 
which comes within the latter division ; but we shall afterwards see that the 
Falco Novce Zelandice, Auct. (the Milvago leucurus of this work) has a naked 
craw, which is largely protruded after the bird has eaten. M. D’Orbigny 
has also instituted the genus Phalcobcenus, to receive a bird of this sub-family, 
with the following characters : 
“ Bee fortement comprime, sans aucune dent ni sinus, k commissure tr6s- 
arquee & son extr6mit6 ; cire along^e et droite ; un large espace nu entourant la 
partie anterieure et inferieure de l’ceil, et s’etendant sur toute la mandibule 
inferieure ; tarses emplum^s sur un tiers de leur longueur, le reste reticule ; 
doigts longs, semblables k ceux des gallinac6s, terminus par les ongles longs, 
deprim6s et elargis, tr&s-peu arques, toujours a extremite obtuse ou fortement 
usee ; ailes de la famille, la troisi&me penne plus longue que les autres.” 
Mr. George R. Gray, however, has pointed out to me that Spix, (in his 
Avium Species Novae) ten years since, made a division in this sub-family, from 
the rounded form of the nostril of one of the species, namely, the M. ochroce- 
phalus of his work, or the Chimac/iima of Azara. And Mr. Gray thinks, that all 
the species may be grouped much more nearly in relation to their affinities by 
this character, than by any other : he further adds ; — “ The only difference 
which I can discover between this latter genus (Milvago), and D’Orbigny ’s 
(. Phalcobcenus ), is, that in the latter the bill is rather longer, and not quite so 
elevated in the culmen as in the former ; and these characters must be considered 
too trivial for the foundation of a generic division. I, therefore, propose to retain 
Spix’s genus, Milvago, for all those Polyborince which possess rounded nostrils with 
