acute, that of hind toe smallest, of middle toe hy much the largest, and having
the inner edge thin and dilated.
Plumage soft, close, blended, very short on the head; the feathers in general broad and rounded. Wings very long, narrow and pointed; primary quills tapering but rounded, the first longest, the rest rapidly graduated; secondary short, broad, rather acute, the inner more tapering. Tail long, very deeply forked, of twelve feathers, of which the outer are tapering, the middle rounded and short.
Bill and feet black. Iris chestnut. Forehead white; lores, upper part of the head, the hind neck and all the upper parts, deep black glossed with blue, excepting the edges of the wings and the lateral tail-feathers, which are white, the latter with the inner web towards the end dusky. All the lower parts and the sides of the neck are pure white.
Length to end of tail I6i inches, to end of wings 15§, to end of claws 11^; extent of wings 34f ; wing from flexure 12; tail to the end 7§, to the fork 3§; bill along the ridge If, along the edge of lower mandible 2/g-; tarsus |f; middle toe ff , its claw T %.
The Female is similar to the male.
Female. The mouth is formed as in the Cayenne Tern; its width 8|- twelfths. Tongue 1 inch 4 twelfths long, emarginate and papillate at the base, very slender, channelled above, horny beneath, tapering to a point. (Esophagus 6| inches long, 1 inch wide at the commencement, 9 twelfths along the neck, but within the thorax dilated into an enormous sac 1 inch 9 twelfths in width. Stomach exceedingly small, being only 10^- twelfths long, 7 twelfths broad; its muscles very thin, the epithelium strong, longitudinally rugous, and of a bright red colour. The belt of the proventricular glands only 3 twelfths in breadth. The walls of the oesophagus are extremely thin, so as to be membranous and transparent. Lobes of liver 1 inch 9 twelfths, and 1 inch 2 twelfths long; gall-bladder ^ inch long, 3 twelfths broad. Intestine 15 inches long, 3 twelfths broad at the commencement, diminishing to 2 twelfths; cceca 1 inch 2 twelfths long, their greatest width 1^ twelfths, at the base only f- twelfth; in form and proportion they are thus like those of the genus Lestris; their distance from the extremity 2 inches, cloaca globular, 9 twelfths in diameter.
Trachea 4 inches long, from 2|- twelfths to lj twelfths in breadth, roundish, the rings 95, unossified. Bronchi very wide, of 28 rings. Mus- cles as in the other species.
