72 BULLETIN OF THE NUTTALL 



Subgenus Craxirex (Gould)," * a group repi'esented most numerously in 

 South America. Two species only (Buteo sioainsoni and B. fennsylvani- 

 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 iniportance 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 different 

 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 bairdii of Hoy, B. insignatus 

 and B. oxypterus of Cassin, and B. fuliginosus of Sclater. 



A little later appeared his " Monograph of the Genus Micrastur," t 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. Ridgvvay, entitled " Second Thoughts on the Genus Micras- 

 tur." J 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 j)aper no allusion. 



During the elaboration of these important papers on the American Fal- 

 conid(e, 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 most cases at least, fallen un- 



* Proc. Acad. Nat. Sci. Phila., 1875, pp. 89-119. 



t Studies of the American Falconidcc: Monograph of the Genus Micrastur. 

 Proc. Acad. Nat. Sci. Phila., 1875, pp. 470-502, figs. 1-9. 



J Ibis, January, 1876, pp. 1-5. 



§ Revision of the Falconine Genera, Micrastur, Geranospiza, and Rupornis, 

 and the Strigine Genus, Glaucidium. Proc. Bost. Soc. Nat. Hist., Vol. XVI, 

 pp. 73 - 81, December, 1873. 



