Bill longer than the head, nearly straight, tetragonal at the base, suddenly extremely compressed and continuing so to the end; upper mandible much shorter than the lower, its ridge sharp, the sides erect but a little convex, the edges approximated so as to leave merely a very narrow groove between them, the tip a little rounded, when viewed laterally; nasal groove rather short, near the margin; lower mandible with the angle extremely short, the dorsal line straight or slightly decurved, the sides erect, obliquely grooved, the edges united into a very thin blade, which fits into the narrow groove of the upper mandible, the tip rounded or abrupt, when viewed laterally. Nostrils linear-oblong. Head rather large, oblong, considerably elevated in front; neck rather short, thick; body short, ovate. Feet short, moderately stout; tibia bare below, with narrow transverse scutella before and behind; tarsus short, anteriorly covered with broad scutella; toes very small, the first extremely short and free, unless at the base; middle toe slightly longer than outer; anterior toes united by deeply emarginate webs. Claws long, compressed, slightly arched, rather obtuse. Plumage moderately full, soft, and blended; wings extremely long, and very narrow; primary quills excessively long, the first longest; secondaries short. Tail of moderate length, deeply forked, of twelve feathers. Tongue short, triangular, tapering; œsophagus wide; stomach rather small, oblong, muscular, the cuticular lining dense, with nine broad longitudinal rugæ; intestine rather long, narrow; cœca very small; cloaca large, globular, the digestive organs are precisely similar to those of the Terns and smaller Gulls. 428. 1. Rhynchops nigra, Linn. Black Skimmer. Plate CCCXXIII. Male Bill rich carmine in its basal half, the rest black; feet carmine; upper plumage deep brownish-black; secondary quills and four or five of the primaries tipped with white, the latter on the inner web chiefly; tail-feathers black, broadly margined on both sides with white, the outer more extensively; the middle tail-coverts black, the lateral black on the inner, and white on the outer web; a broad band of white over the forehead, extending to the fore part of the eye; cheeks and throat of the same colour; the rest of the neck, and lower parts in spring and autumn of a delicate cream-colour; axillary feathers, lower wing-coverts, and a large portion of the secondary quills, white, the coverts along the edge of the wing black. Female smaller, similar to the male, but with the tail-feathers white, excepting a longitudinal band including the shaft. After the first autumnal moult, there is on the hind part of the neck a broad band of white mottled with greyish-black; the lower parts pure white, the upper of a duller black; bill and feet less richly coloured. _Male_, 20, 48. _Female_, 16-3/4, 44-1/2.