A year after this species was first described by Vieillot, under the name of _Procellaria leucorhoa_, it was discovered at St. Kilda by Bullock. This was early in the present century, but the islands, known collectively by that name, still continue to be its most famous breeding place in our area, or even in Europe. Three years after its discovery, it was rechristened _P. leachi_ by the French naturalist Temminck, a name which has found favour with many writers. The Fork-tailed Petrel is known to breed on North Rona, and at some other spots in the Outer Hebrides, as well as on the Blaskets off the coast of Kerry. There can be little doubt that many other breeding stations of this Petrel remain to be discovered. This species, readily distinguished from the Stormy Petrel by its larger size and deeply-forked tail, is rarely seen near the land unless during the breeding season, or when driven thence by boisterous weather. I have known it to be caught in the flight-nets on the mud-banks of the Wash; whilst it is of tolerably frequent occurrence elsewhere off our eastern and southern coasts. In its habits generally it very closely resembles its better known ally, the Stormy Petrel. During the non-breeding season it wanders vast distances from land, sleeping and resting on the sea when tired, following ships for miles, fluttering along close to the ocean, now down into the trough of the wave, anon skimming over the crest to half-fly, half-run, with patting feet, down the smooth surface of the next. Except during the breeding season this Petrel is not very gregarious; it may often be seen in parties of perhaps half-a-dozen, scattered over a considerable surface of water. The exact nature of the food of this species is apparently unknown. It is said, in a vague and general way, to feed on crustaceans and small molluscs, and the scraps of refuse cast from passing vessels, but birds which I have dissected contained similar substances to those found in the Fulmar—a nearly clear oil, mingled with the jaws of cuttlefish, and scraps of sorrel.