The trachea, 4-8/12 inches long, (2-1/2)/12 in diameter above, 2/12 below; of 120 unossified rings; its contractor muscles feeble, the sterno-tracheal moderate; a single pair of inferior laryngeal; the bronchial rings about 15. COMMON TERN. _STERNA HIRUNDO_, LINN. PLATE CCCIX. ADULT. Although the Prince of Musignano has thought that the bird named the Common Tern in America, differs from that bearing the same name in Europe, and has in consequence changed its appellation to that of Wilson’s Tern, I am of opinion that no difference exists between the Common Terns of the two Continents. The cry of both is besides precisely similar, so that with me there is no doubt whatever as to their identity. Experience has shewn me that the markings or white spots on the primary quills of Gulls, at one time assumed as a criterion by which species might be distinguished, cannot in the least be depended on, varying, as they always do, in individuals of the same species, at almost each successive moult. Then why, Reader, should not Terns exhibit analogous changes? The fact is, they do so; and it is almost impossible, on closely inspecting a dozen or more specimens procured at the same period, in either country, to find two individuals exactly corresponding in every particular. Some have the bill almost entirely black, while others have it more or less red and black, and tipped with yellow. The length of the tail-feathers, that of the tarsus, and the size of the inter-digital membranes, are all found to differ in some degree, if minutely compared. If species are to be founded on such slight differences, an ample field is open to those who are ambitious of being discoverers. At all events, I cannot help remarking here, that it seems to me improper to impose new names on objects, until it is proved by undeniable facts that they present permanent differences. I have observed this species along the Atlantic coast of North America, from Galveston Island in Texas to the Straits of Belle Isle on the coast of Labrador, both in spring and in early autumn. But when on the islands in Galveston Bay, in the month of April, I saw only a few arriving there from the west; whereas, in the beginning of May great numbers arrived there from the east, settled at once, and commenced breeding. I felt convinced that the numbers which came from the direction of the Floridas were much greater than those which arrived from the westward, and judged it probable that vast numbers had at the same time left the Peninsula on their way northward. Should other travellers observe the same or similar phenomena at the season mentioned, it will be proved that this species does not extend its autumnal migration so far as several others, which I observed arriving at Galveston Island from the south-west, for example, the Least Tern, _Sterna minuta_, the Cayenne Tern, _St. cayana_, and the Black Tern, _St. nigra_.