In some individuals at this period, the mandibles are of equal length. The palate is flat, with two longitudinal series of papillæ directed backwards. The upper mandible is extremely contracted, having internally only a very narrow groove, into which is received the single thin edge of the lower mandible. The posterior aperture of the nares is 1-5/12 inch long, with a transverse line of papillae at the middle on each side, and another behind. The tongue is sagittiform, 6-1/2 twelfths long, with two conical papillae at the base, soft, fleshy, flat above, horny beneath. Aperture of the glottis 4-1/2 twelfths long, with numerous small papillae behind. Lobes of the liver equal, 1-1/2 inch long. The heart of moderate size, 1-1/12 long, 10 twelfths broad. The œsophagus, of which only the lower portion, _a_, is seen in the figure, is 8 inches long, gradually contracts from a diameter of 1 inch to 4 twelfths, then enlarges until opposite the liver, where its greatest diameter is 1-4/12. Its external transverse fibres are very distinct, as are the internal longitudinal. The proventriculus, _b_, is 9 twelfths long, its glandules extremely small and numerous, roundish, scarcely a quarter of a twelfth in length. The stomach, _c_, _d_, _e_, is rather small, oblong, 1 inch 4 twelfths long, 11 twelfths broad, muscular, with the lateral muscles moderate. The cuticular lining of the stomach is disposed in nine broad longitudinal rugae of a light red colour, as in the smaller Gulls and Terns. Its lateral muscles are about 4 twelfths thick, the tendons, _e_, 6 twelfths in diameter. The intestine is 2 feet 4 inches long, its average diameter 2-1/2 twelfths. The rectum is 2 inches long. One of the cœca is 4, the other 3 twelfths, their diameter 1-1/4 twelfths. In another individual, the intestine is 22-1/2 inches long; the cœca 5 twelfths long, 1 twelfth in diameter; the rectum 1-3/4 inch long; the cloaca 9 twelfths in diameter. [Illustration] The trachea is 5-3/4 inches long, round, but not ossified, its diameter at the top 5 twelfths, contracting gradually to 2-1/2 twelfths. The lateral or contractor muscles are small; the sterno-tracheal slender; there is a pair of inferior laryngeals, going to the last ring of the trachea. The number of rings is 90, and a large inferior ring. The bronchi are of moderate length, but wider, their diameter being 3-1/2 twelfths at the upper part; the number of their half-rings about 18. The digestive organs of this bird are precisely similar to those of the Terns and smaller Gulls, to which it is also allied by many of its habits. BONAPARTIAN GULL. _LARUS BONAPARTII_, SWAINS. PLATE CCCXXIV. MALE, FEMALE, AND YOUNG.