Family	DELAFIELD'S GROUND-WARBLER. [Masked Yellowthroat.]
Genus	TRICHAS DELAFIELDII, Aud. [Geothlypis aequinoctiali.]

This beautiful little bird I named in honour of Colonel DELAFIELD, President of the Lyceum of Natural History in the city of New York, a gentleman distinguished by his scientific attainments, not less than by those accomplishments and virtues which tend to improve and adorn society. It so much resembles the Maryland Yellow-throat, (Trichas Marilandica,) Sylvia Trichas of the older authors, Trichas personatus of SWAINSON, that one might readily confound the two species. The differences between them will be easily seen on comparing their descriptions. The only specimen in my possession was obtained from Mr. TOWNSEND, who procured it in California.

DELAFIELD'S YELLOW-THROAT, Sylvia Delafieldii, Aud. Orn. Biog., vol. v.p. 307.

Bill longish, nearly straight, conico-subulate, rather broader than high at the base, compressed toward the end, acute; upper mandible with the dorsal line declinato-convex, the ridge narrow, the sides convex, the edges direct and overlapping, with a very slight notch, the tip narrow; lower mandible with the angle of moderate length and narrow, the dorsal line ascending and straight, the sides rounded, the edges inflected, the tip acute; the gape-line considerably arched. Nostrils basal, lateral, oblong, operculate, exposed.

Head of moderate size, ovate; neck short; body moderately stout. Feet rather long, tarsus slender, longer than the middle toe, much compressed, covered anteriorly with seven scutella, behind with two longitudinal plates meeting so as to form a thin edge; the lateral toes nearly equal, the third much longer, and united at the base to the fourth, the hind toe large; claws moderately arched, extremely compressed, with the sides faintly grooved, acute.

Plumage soft and blended with little gloss. Wings rather long, somewhat concave; the second, third, and fourth primaries have the outer web cut out towards the end; the first quill is three and a half twelfths shorter than the second, which is two-twelfths shorter than the third; the latter is longest, but scarcely exceeds the fourth, and the fifth is only a quarter of a twelfth shorter than it; the other primaries very slowly graduated, the longest or third being only five-twelfths longer than the first secondary; all the quills are rounded. Tail rather long, straight, much rounded, the lateral feathers being half an inch shorter than the middle.

Upper mandible blackish-brown, with the edges yellowish flesh-colour; lower mandible of the latter colour, slightly dusky at the point. A band of black passes across the forehead, includes the loral space and eyes, and terminates on the car-coverts. The upper part of the head is light greyish-blue, tinged behind with green; the rest of the upper parts dull greyish-olive; the quills and tail-feathers wood-brown, the edge of the wing, and the margin of the outer primary, yellow. The fore part of the neck, and all the lower parts, rich yellow, excepting the sides, which are shaded into dull yellowish-green, and the lower wing-coverts and axillaries, which are nearly white.

Length to end of tail 5 1/4 inches; bill along the ridge along the edge of lower mandible 8/12; wing from flexure 2 5/12; tail 2 1/2; tarsus 11/12; hind toe (4 3/4)/12, its claw (4 1/2)/12; middle toe (7 1/2)/12, its claw 3/12.

This species has the bill much stronger and more elongated than Trichas Marilandica; its wings are much more rounded, the first quill being nearly five-twelfths shorter than the third, whereas in the latter, it is scarcely a twelfth and a half shorter; its tail is more rounded; and its tarsi and toes are proportionally larger. The colours are, however, similar; but the present species has no whitish band margining the black band on the head, and this latter band is much narrower in front, and does not proceed so far down the neck, extending only to the distance of four and a half twelfths from the eye, whereas in T. Marilandica it extends to the distance of half an inch.