Bill shorter than the head, rather higher than broad at the base, somewhat conical, depressed towards the end, rounded at the tip. Upper mandible with the dorsal line sloping, the ridge broad and flattened, the sides sloping, the edges soft and obtuse, the oblique marginal lamellæ short, transverse, about thirty on each side; the unguis obovate, convex, denticulate on the inner edge. Nasal groove oblong, parallel to the ridge, filled by the soft membrane of the bill; nostrils medial, lateral, longitudinal, narrow-elliptical, open, pervious. Lower mandible straight, with the angle very long, narrow, and rounded, the edges soft and obtuse, with about thirty oblique lamellæ on a perpendicular plane.
Head small, oblong, compressed. Neck long and slender. Body full, slightly depressed. Feet short, stout, placed behind the centre of the body; legs bare a little above the tibio-tarsal joint; tarsus short, a little compressed, covered all round with angular reticulated scales, which are smaller behind; hind toe very small, with a narrow membrane; third toe longest, fourth a little shorter, but longer than second; all the toes reticulated above at the base, but with narrow transverse scutella towards the end; the three anterior connected by a reticulated membrane, the outer with a thick margin, the inner with the margin extended into a two-lobed web; claws small, arched, rather compressed, except that of the middle toe, which is bent obliquely outwards and depressed, with a curved edge. Wings of moderate length, with an obtuse protuberance at the flexure.
Plumage close, rather short, compact above, blended on the neck and lower parts of the body. The feathers of the head and neck very narrow, of the back very broad and abrupt, of the breast and belly broadly rounded. Wings, when closed, extending to about an inch from the end of the tail, acute; primaries very strong, curved, the second longest, the third slightly shorter, the first almost as long as the third, the rest rapidly graduated; secondaries long, rather narrow, rounded. Tail very short, rounded, of eighteen stiff, rounded, but acuminate, feathers.
Bill, feet, and claws black. Iris chestnut-brown. Head and two upper thirds of the neck glossy black; forehead, cheeks, and chin, tinged with brown; lower eyelid white; a broad band of the same across the throat to behind the eyes; rump and tail-feathers also black. The general colour of the rest of the upper parts is greyish-brown, the wing-coverts shaded into ash-grey; all the feathers terminally edged with very pale brown; the lower part of the neck passing into greyish-white, which is the general colour of the lower parts, with the exception of the abdomen, which is pure white, the sides, which are pale brownish-grey, the feathers tipped with white, and the lower wing-coverts, which are also pale brownish-grey. The margins of the rump, and the upper tail-coverts, pure white.
In very old males, I have found the breast of a fine pale buff.
Length to end of tail 43 inches, extent of wings 65; bill along the ridge 2 1/2, in depth at the base 1 2/12, in breadth 1; tarsus 3 7/12; middle toe and claw 4 1/4; wing from flexure 20; tail 7 1/2. Weight 7 lb.
Adult Female. Plate CCI. Fig. 2.
The Female is somewhat less than the male, but similar in colouring, although the tints are duller. The white of the throat is tinged with brown; the lower parts are always more grey, and the black of the head, neck, rump, and tail, is shaded with brown.
Length 41 inches. Weight 5 3/4 lb.