Studies on cetaceans at Argentina, Uruguay and Brazil can be divided in three periods. During the first one (1861-1963), studies of the Argentines Burmeister, Gallardo, Lahille and Marelli were done on dolphin and porpoise osteology, occasionally on whales, these wire followed by those of Miranda Ribeiro and Carvalho in Brazil. The second period (1969-1976) begins with the studies of the North Américan Gilmore (1969) in Patagonia. From this year on, numerous forcing expeditions came to Argentina and Uruguay, to study the right whale, Eubalaena australis behavior in Patagonia and the La Plata river dolphin. Pontoporia blainvillei biology at Punta del Diablo, Uruguay. These expeditions have contributed to a better knowledge of whales and dolphins, not only in South if not also, abroad. During thin period studies on bekzvior, bioacustics, population dynamics and bio-ecological studies ; began. Simultaneously it is observed that Latin Americm researches, specially those of Uruguay and Brazil, become interested ind doing cetological research on systematic aspects. The third period (1976- ) it is characterized by an increased effort on this field and also by a better exchange of information between the three S. W. Atlantic countries. In Brazil, during the last two years, a gret interest on the minke whale conservation problem has developed, not only at the public opinion, but also at the government level.

A female Blainville's beaked whale, Mesopiodon densirostris, 4.4m long was found stranded at 42km, South of Cassino, Rio Grande do Sul, Brazil. The triangular shape and dimensions of the pair of unerupted teeth (60 x 45 x 11 mm) in the lower jaw, together with the distance (180mm) from the alveoli to the hinder edge of the mandibular symphysis proved to be a good systematic character for females of this species. The vertebral formula is C 7 + D 10 + L 11 + Ca 15 (+2) =45. It presents 10 pairs of ribs, 6 being double headed. M. densirostris is the only species of Mesopiodon which seems normally to occur both north and south of the equator and also the onlv species of this genus to strand on oceanic island of tropical and warm-temperature waters. The present record is the first for the Soutn West Atlantic waters.

Menella coeruieoalba is a dolphin widely distributed in temperate and tropical waters. This species is recorded for our marine fauna on the basis of a 2.35 m long specimen found at 20 km North of the East rocky jetty on the access channel into Lagoa dos Patos, RS, (MORG 064) and also from a sightning in front of Santa Catarina coast. Its vertebral formula is: C 7 + D 14 + L 21 + Ca 34 = 76, with 23 Chevron bones. The number of alveoli is 48-48 / 43-42, its presents 14 pairs of ribs, 8 of them double-headed. The skull measurements of this specimen are compared with other three from the Southern Hemisphere. Through colour slides obtained in front of Rio de Janeiro coasts, Steno bredanensis was recorded. This dolphin also presents a wide distribution similar to the previous species. During the first cruise of the R/V "Atlântico Sul" two pods of the spotted dolphin, Stenella cfr. plagiodon were sighted and photographed. This species can be easily identified on the basis of the clear brown tegument with numerous white rounded spots, in adults. One of the skull (MCNRS 026) studied may belong to this species.