SP. CHAR. _Immature?_ (41,703, “California”; F. Gruber). Outstretched feet reaching beyond tail. General plumage dull dark-bistre, with a grayish-umber cast in some lights, darkest on the head above and back; the posterior lower parts paler and more reddish; throat and neck much tinged with pale rusty (this obsoletely bordering the feathers, which here have fine whitish filaments attached to the shafts); primaries uniform black. Tail like the rump, but with a more hoary tinge (not paler at the tip), and crossed with seven or eight very narrow obscure bars of darker, the last of which is distant an inch or more from the end. Lining of wing dark bistre, much tinged with rusty, this prevalent toward the edge; under surface of primaries white anterior to their emargination, beyond which they are ashy, approaching black at ends; ashy portion with distant, very obsolete, dusky bars, but the cheeks and throat streaked obsoletely with this color. No distinct white anywhere about the head or neck. Wing, 10.00; tail, 5.80; tarsus, 2.70; middle toe, 1.40; inner, .90; outer, 1.10; posterior, .80; hind claw, 1.00 (chord); inner claw, .91; on front of tarsus, twelve exposed large transverse scutellæ; only 1.70 of the tarsus exposed. The type of this species still remains unique. It was sent to the Smithsonian Institution by Mr. Gruber, who labelled it as having been obtained in California. Nothing is known of its habits. GENUS BUTEO, CUVIER. _Buteo_, CUV. 1799. (Type, _Falco buteo_, LINN. = _Buteo vulgaris_, BECHSTEIN.) _Craxirex_, GOULD, 1838. (Type, _Buteo galapagoensis_, GOULD.) _Pæcilopternis_, KAUP, 1847. (Type, _Falco borealis_, GM.) _Tachytriorchis_, KAUP, 1844. (Type, _Falco pterocles_, TEMM.) GEN. CHAR. Form robust and heavy, the wings long, and rather pointed, the tail moderate and rounded, the bill and feet strong. Bill intermediate between that of _Astur_ and that of _Parabuteo_. Wing long and rather pointed, the third to fifth quill longest, the first shorter than eighth; three to four with inner webs emarginated. Tail moderate, slightly rounded. [Illustration: =1750=, ♀. ½ =1750=, ♀. =10571=, ♀. ½ =10571=, ♀. ¼ _Buteo borealis_ (1750; 10571).] [Illustration: =52763=, ♂. ½ _Buteo zonocercus_ (52763).] [Illustration: =58505=, ♀. ¼ _Buteo swainsoni_ (58505).] The species of this genus are very numerous, especially within the tropics, and are found all over the world, except in Australia. About thirty nominal species are known, of which about fifteen distinct species, not including geographical races, belong to America. A single species, _B. solitarius_ (_Pandion solitarius_, Peale), (Gray’s Hand List, I, 15, No. 136,) belongs to the Sandwich Islands. The genus seems to be wanting in the Australian and East Indian regions. The following species and races belong to the North American fauna. Species and Races. =A.= Three outer primaries with their inner webs cut or emarginated.