I regret to say that I am not sufficiently acquainted with this singular species to give any account of its habits and economy, but, judging from the feebleness of its bill and talons and the shortness of its tarsi, I conceive that it principally preys upon insects and their larvæ; and it is not improbable that honey and the larvæ of bees and ants, which abound in Australia, may form a portion of its food. Any information on this head that may have been ascertained by residents in Australia would, if made known, be of the highest interest to ornithologists, as an addition to the history of this singular form among the _Falconidæ_. Its extreme rarity, however, will, I fear, tend much to prevent the acquirement of this desirable information. I saw it soaring high in the air over the plains in the neighbourhood of the Namoi, but never sufficiently near to admit of a successful shot. All the specimens I have seen were collected either at Moreton Bay or on the banks of the Clarence. As little or no difference exists in the plumage of the specimens I have examined, I presume that the sexes are very similar. Crown of the head, sides of the face, ear-coverts, and upper part of the back brownish grey; occiput and lengthened occipital plumes blackish brown; back and scapulars brown; wings uniform dark brownish grey above, beneath silvery grey; primaries and secondaries crossed by several bands, and largely terminated with black; rump and upper tail-coverts chocolate-brown; tail brownish grey above, lighter beneath, crossed by three narrow bands of black near the base, and deeply terminated with the same colour; throat, chest, part of the shoulder, and under tail-coverts greyish white tinged with rufous; abdomen, flanks and thighs buffy white, crossed with conspicuous narrow bands of reddish chestnut; bill bluish horn-colour; tarsi yellowish. The Plate pourtrays the bird of the natural size. [Illustration: CIRCUS ASSIMILIS: _Jard. & Selb._ _J. Gould and H. C. Richter del et lith._ _C. Hullmandel Imp._ ] CIRCUS ASSIMILIS, _Jard. and Selb._ Allied Harrier. _Circus assimilis_, Jard. and Selb. Ill. Orn., vol. ii. pl. 51. _Swamp Hawk_, of the Colonists.