The velocity with which these Humming Birds glance through the air is extraordinary, and so rapid is the vibration of their wings, that their movement eludes the sight; when hovering before a flower, they seem suspended as if by some magic power. THE SICKLE-BILLED HUMMING BIRD. The SICKLE-BILLED HUMMING BIRD (_Eutoxeres aquila_) principally differs from its congeners in the sickle-shaped formation of its powerful beak and its conical tail. In this species the back is of a glossy greyish green; the head and a small crest by which it is adorned are brownish black, these feathers and those upon the rump being edged with brown; the under side is brownish black, marked on the throat with greyish yellow and on the breast with white spots; the quills are purplish brown, the exterior secondaries tipped with white. "It is evident," says Gould, "that the bill of this very rare and singular Humming Bird is adapted for some especial purpose, and we may readily infer that it has been expressly formed to enable this species to obtain its food from the deep and remarkably-shaped blossoms of the various orchidaceous and other plants, with curved, tubular flowers, so abundant in the country the bird inhabits, and for exploring which a bill of any other form would be useless." At present nothing is known of its habits. * * * * * The SUN BIRDS (_Phaëtornis_) have a large, long head and slightly-curved beak. Their foot is small and delicate, with partially feathered tarsus and formidable claws; the tail, in which the centre feathers far exceed the rest in length, is long and conical. The plumage is dull, and the sexes alike in colour, the only difference observable being the formation of the tail. THE CAYENNE HERMIT. The CAYENNE HERMIT (_Phaëtornis superciliosus_) is about seven inches long; the wing measures two inches and one-third, and the tail two inches and two thirds. In this species the mantle is of a pure metallic green, and the under side reddish grey; the feathers on the back have reddish yellow borders; a pale reddish yellow line passes above and below the eye; the quills are brown, shaded with violet; the centre tail-feathers, which are twice the length of those at the sides, are of a dull metallic green, shading into black towards the white tip, and edged with reddish yellow; the upper mandible is black, and the lower half of the under one pale yellow; the feet are flesh-pink. The female has quieter plumage and a shorter tail; the latter is but slightly wedge-shaped, and fully two inches less than that of her mate.