The species of this genus are especially characterized by their long, attenuated primaries, their moderately forked or nearly even tail, and the concealed colored crest in the crown. Their affinities are nearest to Milvulus, from which the tail, shorter than the wings, instead of twice as long, or more, will always serve as a point of distinction. The attenuation of the primary differs in being less abrupt, and not truly linear, sloping gradually, and not bounded behind by a notch. We are unable to appreciate any other differences of importance.
The character and extent of the attenuation of the primaries, the depth of the fork of the tail, with the size of the legs and bill, all vary considerably, and may, perhaps, serve as ground for further subdivisions. The bill, in particular, varies much in size in the North American species, from that of
T. carolinensis, where the culmen is but little more than half the head, to that of T. dominicensis (genus Melittarchus of Cabanis), where it is decidedly longer than the head, and almost as stout as that of Saurophagus.
The North American species of Tyrannus (with their nearest Mexican allies) may be arranged by colors, accordingly as they are white beneath or yellow, in the following manner:—
A. Under parts whitish, without any shade of yellow. A faint grayish-plumbeous pectoral band.
1. T. carolinensis. Tail slightly rounded. Bill much shorter than the head. Above black, shading into dark plumbeous on the back. Tail abruptly and broadly margined and tipped with pure white. (Tyrannus.) Hab. Whole of North America, north to the British Provinces, and south to Panama. Rare in the Western Province of North America.
2. T. dominicensis. Tail moderately forked. Bill longer than the head. Above gray; the tail and wings brownish. The edges and tips of the tail narrowly margined with soiled white. (Melittarchus.) Hab. West Indies, New Granada, Panama, Florida, Georgia, and South Carolina.
B. Above ashy-olive, becoming purer ash on the head. Tail brown or black. Beneath yellow; the chin paler; the breast strongly shaded with olivaceous or ashy. (Laphyctes.)
a. Tail nearly black; the outer edges of the outer webs of the feathers with the fibres united closely throughout, and colored similarly to the rest of the feathers; beneath sulphur-yellow.
3. T. verticalis. Tail slightly forked; external feather with the entire outer web and the outer half of the shaft abruptly yellowish-white. Pectoral band pale ashy, lighter than the back. Hab. Western Province of United States.