Bill about the length of the head, slender, tapering, much compressed,
nearly straight, extremely attenuated towards the end. Upper mandible
with the dorsal line slightly arched, the ridge rather broad and convex at the
base, narrow towards the end, the sides nearly erect, the edges sharp and
direct. Nasal groove short, extending to a fourth of the length of the bill;
nostrils basal, linear, direct, pervious. Lower mandible with the angle
extremely narrow, very acute, extending to the middle, the dorsal line
straightish, the sides erect, the edges sharp and inflected, the tip extremely
acute.
Head of moderate size, ovate; neck short; body very slender; feet small. Tibia bare below; tarsus very short, slender, compressed, covered anteriorly with small scutella, laterally and behind with reticular scales; toes small, slender, the first extremely small, the third longest, the fourth considerably shorter, all scutellate above, the anterior united by reticulated webs having a deeply concave margin. Claws arched, compressed, acute, that of hind toe smallest, of middle toe by much the largest, and having its inner edge thin and dilated.
Plumage soft, close, blended, very short on the fore part of the head; the feathers in general broad and rounded. Wings very long, narrow, and pointed; primary quills tapering, straight, the first longest, the next five- twelfths of an inch shorter, the rest rapidly graduated; secondary quills short, broad, incurved, narrowed towards the end, the inner straight. Tail rather long, very deeply forked, the lateral feathers extending an inch and seven-twelfths beyond the fork.
Bill light yellowish-orange, its tips black, but the extreme points horn- colour. Iris hazel; feet light orange-red, the bare part of the tibia dusky- claws black. On the forehead, a triangular white patch extending to the middle of the eye; upper part of the head and the nape, with a line from the eye to the bill, deep black; sides of the head, fore-neck and lower parts, pure white; back and wings very pale bluish-grey; first two quills with the outer web greyish-black, and rather less than half of their inner web of the same colour, the rest white, extending to about half an inch from their extremities. Tail white in summer, of a paler tint than the back at other times.
Length to end of tail Sf- inches, to end of wings 9^, to end of claws 7^, to end of shortest tail-feathers 7; extent of wings ISf; wing from flexure 6y|; tail 3^; bill along the ridge 7^ twelfths, along the edge of lower man- dible l T 5 f ; tarsus ^; middle toe T 7 2, its claw T 3 2.
The Female is a little smaller than the male, but otherwise similar. Young fledged.
Bill greenish-black. Iris dusky. Feet pale yellowish-orange. All the
