The Gulls and Terns of the Rio de la Plata require more attention, and it is probable that several additions will have to be made to the list. At present we can enumerate only nine species as certainly found within our limits. The number of known Neotropical Laridæ is about thirty-three. 410. RHYNCHOPS MELANURA, Sw. (BLACK-TAILED SKIMMER.) +Rhynchops nigra+, _Burm. La-Plata Reise_, ii. p. 520 (Rio Paraná); _Scl. et Salv. P. Z. S._ 1869, p. 634 (Buenos Ayres); _iid. Nomencl._ p. 147; _Durnford, Ibis_, 1877, p. 209 (Buenos Ayres); _White, P. Z. S._ 1882, p. 628 (Buenos Ayres). +Rhynchops melanura+, _Saunders, P. Z. S._ 1882, p. 522. _Description._--Above brownish black; forehead and wing-band white; tail black: beneath white; bill, apical half black, basal half orange; feet red: whole length 19·0 inches, wing 15·0, tail 5·0. _Female_ similar. _Hab._ Coasts of South America. The Black-tailed Skimmer, which is common on the coasts of Brazil, migrates south in spring, following the course of the Plata river in its journey, and appearing in pairs or small flocks in the neighbourhood of Buenos Ayres during the month of October. Its chief breeding-ground is on the extensive mud-banks and islets at Bahia Blanca on the Atlantic coast. The return-migration occurs in March. Darwin met with the Scissor-bill during his excursion up the Paraná in October 1833, and speaks of it as follows (Nat. Journ. p. 161):-- "I here saw a very extraordinary bird, called the Scissor-beak (_Rhynchops nigra_). It has short legs, web feet, extremely long-pointed wings, and is of about the size of a Tern. The beak is flattened laterally, that is in a plane at right angles to that of a Spoonbill or Duck. It is as flat and elastic as an ivory paper-cutter, and the lower mandible, differently from every other bird, is an inch and a half longer than the upper. I will here detail all I know of the habits of the Scissor-beak. It is found both on the east and west coasts, between lat. 30° and 45°, and frequents either salt or fresh water. The specimen now at the Zoological Society was shot at a lake near Maldonado, from which the water had been nearly drained, and which, in consequence, swarmed with small fry. I there saw several of these birds, generally in small flocks, flying backwards and forwards, close to the surface of the lake. They kept their bills wide open, and with the lower mandible half buried in the water. Thus skimming the surface, they ploughed it in their course; the water was quite smooth, and it formed a most curious spectacle to behold a flock, each bird leaving its narrow wake on the mirror-like surface. In their flight, they frequently twist about with extreme rapidity, and so dexterously manage, that with their projecting lower mandible they plough up small fish, which are secured by the upper half of their scissor-like bill. This fact I repeatedly saw, as, like