72 
BULLETIN OF THE NUTTALL 
Subgenus Graxirex (Gould)/’ * a group represented most numerously in 
South America. Two species only (Buteo swainsoni and B. pemisylvani- 
cus), of the six referred to this subgenus, range far into North America. 
This group is distinguished from the ordinary Buteones by having only 
three (instead of four) of the outer primaries emarginated on their inner 
webs. While agreeing in this feature, they vary considerably in respect 
to the relative length of the wing, the size and length of the tarsus, and 
in other details of structure ; and it is perhaps an open question whether 
our author does not place too much importance upon what he regards as 
the distinctive feature of the group, namely, the number of emargi- 
nated primaries. The various phases of plumage presented by the dilferent 
species is described in considerable detail, with very full citations of syn- 
onymy. The account of Buteo swainsoni is particularly full, nearly one 
half the paper (about fifteen pages) being devoted to this species alone. 
Among its prominent synonymes are Buteo hairdii of Hoy, B. insignatus 
and B. oxypterus of Cassin, and B. fuliginosus of Sclater. 
A little later appeared his “ Monograph of the Genus Micrastur,” f of 
which seven species are recognized, and of which are given detailed de- 
scriptions. The group is mainly restricted to Central and Northern South 
America, being pre-eminently tropical in distribution. While the species 
are said to present “ no appreciable sexual variation,” they exhibit “ two 
well-marked growth-stages,” the young birds generally greatly differing 
from the adult. In addition to this, several of the species are dimorphic, 
being subject to erythrism, analagous to the dimorphism met with in Syr- 
nium aluco of Europe, in Scops asio, and in the several species of Glaucid- 
ium, among the Owls. * Shortly after this appeared another paper on this 
genus, by Mr. Ridgway, entitled “ Second Thoughts on the Genus Micras- 
tu7\” This is mainly a summary of his “ Monograph.” The “ Second 
Thoughts” relate to his earlier revision of this genus, published in 1873, § 
— in which only five, instead of seven, species were admitted, — rather 
than to the “ Monograph,” to which there is in this paper no allusion. 
During the elaboration of these important papers on the American Fal- 
conidce, Mr. Ridgway has had access to the material contained in all the 
larger public and private ornithological collections of the United States, 
and has been kindly favored with the use of specimens from abroad. He 
has in this way been able to base his investigations upon the examination 
of a larger amount of material than has, in naost cases at least, fallen un- 
^ Proc. Acad. Nat. Sci. Phila., 1875, pp. 89 - 119. 
t Studies of the American Falconidoe : Monograph of the Genus Micrastur. 
Proc. Acad. Nat. Sci. Phila.> 1875, pp. 470-502, figs. 1 -9. 
X Ibis, January, 1876, pp. 1-5. 
§ Revision of the Falconine Genera, Micrastur, Geranospiza, and Rupomis, 
and the Strigine Genus, Glaucidium, Proc. Bost. Soc. Nat. Hist., Yol. XVI, 
pp. 73-81j December, 1873. 
