This bird was first noticed by the celebrated Pennant, in Arctic Zoology, Vol. II., p. 255, who called it the “Fork-tailed Petrel.” An accurate description is given by him, but no further account of it than merely stating “taken among the ice between Asia and America.” On the faith of this description, Gmelin, in _Systema Naturæ_, as cited below, gave the scientific name. Subsequently, Pallas mentions it as an inhabitant of the coasts of Unalaschka and of the Kurile Islands. It is also mentioned in the Zoology of the Voyage of the Sulphur, (London, 1844,) and very handsomely figured from specimens obtained at Sitka in Russian America. To the journal of Dr. Pickering we have again to acknowledge our obligations for a notice of this bird. First recording its occurrence on the 26th of April, 1840, at sea, the distance from the coast of Oregon being about 200 miles, he subsequently mentions it under date of 29th of the same month, as follows: “In sight of the coast of Oregon. Great numbers of the gray _Thalassidroma_ are to-day flitting around and in the track of the vessel, very actively engaged in searching for particles of food thrown overboard. Generally, this bird reminds us of _T. Wilsonii_, but the wings seem longer, and its movements appear to be more rapid, and in fact more like that of the larger Petrels, (_Procellaria_.) It occasionally sails in its flight, but for the greater part moves by very rapidly flexing its wings in the same manner as the species mentioned. “These birds proved not difficult to capture, and several specimens were taken with a hook and line. They would dive a foot or two after the bait, and made use of their wings in and under the water, from which they apparently had not that difficulty in rising observable in the Albatrosses. Though their powers of swimming seemed rather feeble, they alighted in the water without hesitation. The dead body of one of their companions being thrown overboard, they clustered around it with as much avidity as around any other food. “The specimens obtained agree generally in color of plumage, being nearly a uniform pale gray, with the abdomen sometimes paler or nearly white, and generally showing a lighter bar across the wing, when expanded. Uttered a faint note when taken on board.” At present we have no further information relating to this interesting species. DESCRIPTION AND TECHNICAL OBSERVATIONS. Genus Thalassidroma. Vigors. Zool. Jour. II., p. 405. (1825.) Size small; bill rather wide at base, compressed towards the end, and abruptly hooked; lower mandible shorter; nostril elevated, tubular; wings long, pointed, second quill usually longest; tail moderate, rather wide, usually emarginate or forked; legs long, slender; tibiæ more or less naked above the joint with the tarsi; toes rather short, fully webbed. A genus comprising about twelve species, all of which are strictly marine, and inhabit the various oceans of the world.