Swallows, they continued to fly backwards and forwards, close before me. Occasionally, when leaving the surface of the water their flight was wild, irregular, and rapid; they then also uttered loud, harsh cries. When these birds are fishing, the length of the primary feathers of the wings is seen to be quite necessary, in order to keep the latter dry. When thus employed, their forms resemble the symbol by which many artists represent marine birds. The tail is much used in steering their irregular course. "These birds are common far inland along the course of the Rio Paraná; it is said they remain during the whole year, and breed in the marshes. During the day they rest in flocks on the grassy plains, at some distance from the water. Being at anchor, as I have said, in one of the deep creeks between the islands of the Paraná, as the evening drew to a close, one of these Scissor-beaks suddenly appeared. The water was quite still, and many little fish were rising. The bird continued for a long time to skim the surface, flying in its wild and irregular manner up and down the narrow canal, now dark with the growing night and the shadows of the overhanging trees. At Monte Video I observed that some large flocks during the day remained on the mud-banks at the head of the harbour, in the same manner as on the grassy plains near the Paraná; and every evening they took flight direct to seaward. From these facts, I suspect that the _Rhynchops_ generally fishes by night, at which time many of the lower animals come most abundantly to the surface. M. Lesson states that he has seen these birds open the shells of the _Mactræ_, buried in the sand-banks on the coast of Chile; from their weak bills, with the lower mandible so much produced, their short legs and long wings, it is very improbable that this can be a general habit." 411. PHAËTHUSA MAGNIROSTRIS (Licht.). (GREAT-BILLED TERN.) +Sterna magnirostris+, _Burm. La-Plata Reise_, ii. p. 519 (Rio Paraná); _Saunders, P. Z. S._ 1876, p. 643; _Barrows, Auk_, 1884, p. 316 (Entrerios). +Phaëthusa magnirostris+, _Scl. et Salv. Nomencl._ p. 147; _iid. P. Z. S._ 1871, p. 567; _Durnford, Ibis_, 1877, p. 200 (Buenos Ayres). _Description._--Crown, ear-coverts, and nape black; mantle slate-grey, passing into white at the tips of the secondaries; wing-coverts white; quills black; tail slate-grey; lores and entire underparts glossy white; bill yellow, with a greenish tinge at the base of under mandible; legs and feet olive-yellow: whole length 14·5 inches, wing 11·5. In the young the crown is grey; the mantle browner grey. _Hab._ Coasts and rivers of South America. This large-billed Tern, "with a slightly forked tail, but amply developed feet," is occasionally seen near Buenos Ayres.