This gull abounds in flocks on the Pampas, sometimes even as much as fifty and sixty miles inland. Near Buenos Ayres, and at Bahia Blanca, it attends the slaughtering-houses, and feeds, together with the Polybori and Cathartes, on the garbage and offal. The noise which it utters is very like that of the common English gull (_Larus canus_, Linn.) XEMA (CHROICOCEPHALUS) CIRROCEPHALUM. _G. R. Gray._ Larus cirrocephalus, _Vieill._ Nov. Dict. d’Histoire, 21. p. 502. Larus maculipennis, _Licht._ Cat. 83. sp. 855. Larus glaucodes, _Meyen_, Nov. Act. 1839, p. 115. pl. 24. Mouette cendréc, _Azara_, No. 410. This species so closely resembles the _Xema ridibundum_, Boie, that Mr. Gould observes, he should have hardly ventured to have characterized it as distinct; but as M. Vieillot and Meyen have deemed this necessary, he adopts their view. I have compared a suite of specimens, which I procured from the Rio Plata, the coast of Patagonia, and the Straits of Magellan, with several specimens of the _Xema ridibundum_; the only difference which appears to me constant, is that the primaries of the _X. cirrocephalum_, in the adult winter plumage, both of male and female, are tipped with a white spot (a character common to some other species), whereas in the _X. ridibundum_ the points are black. The beak of the latter species, especially the lower mandible, is also a little less strong, or high in proportion to its length. In the immature stage, I could perceive no difference whatever in the plumage of these birds. The proportional quantity of black and white in the primaries, given by Meyen as the essential character, varies in the different states of plumage. The specimens described by this author were procured from Chile.[30] The soles of the feet of my specimens were coloured, deep “reddish orange,” and the bill dull “arterial blood red” of Werner’s nomenclature. In the plains south of Buenos Ayres I saw some of these birds far inland, and I was told that they bred in the marshes. It is well known that the blackheaded gull (_Xema ridibundum_), which we have seen comes so near the _X. cirrocephalum_, frequents the inland marshes to breed. It appears to me a very interesting circumstance thus to find birds of two closely allied species preserving the same peculiarities of habits in Europe and in the wide plains of S. America. Near Buenos Ayres this gull as well as the _L. dominicanus_ sometimes attends the slaughter-houses to pick up bits of meat. RHYNCHOPS NIGRA. _Linn._