The southern boundaries of Tozeuma serratum A. Milne Edwards, Salmoneus ortmanni (Rankin) and Processa profunda Manning & Chace, previously known only from the northwestern Atlantic, have been extended to São Paulo, Paraná and Uruguay, respectively. Latreutes parvulus (Stimpson), previously not known beyond São Paulo has been found to as far south as the Province of Buenos Aires. A systematic account of these four species is furnished, based mainly on material collected by the R/V "Prof. W. Besnard". The 16 species of Alpheoidea whose southern boundaries occur in warm-temperate shelf waters of eastern South America belong to two distinct faunal assemblages: (1) Tropical species - Alpheus floridanus Kingsley, A. intrinsecus Bate, A. normanni Kingsley, Salmoneus ortmanni (Rankin) Synalpheus longicarpus (Herrick), Ogyrides alphaerostris (Kingsley) (= O. occidentalis(Ortmann)), Exhippolysmata oplophoroides (Holthuis), Latreutes parvalus (Stimpson), Processa bermudensis (Rankin) and P. hemphilli Manning & Chace - which are largely restricted to coastal and inshore shelf waters less than 50 m deep; and (2) Subtropical species - Alpheus pouang Chris toffersen, A. puapeba Christoffersen, Merhippolyte americana Holthuis, Tozeuma serratum A. Milne Edwards, Processa guyanae. Holthuis and P. profunda Manning & Chace - which are largely restricted to the outer portion of the continental shelf within the studied area. Considering the temperature and distributional data available for each species, it is suggested that the poleward boundaries of O. alphaerostris are set by maximum summer temperatures of about 20ºC required for the reproduction of the species, while the poleward boundaries of most of the tropical and subtropical species are set by minimum winter temperatures critical for their survival: about 15ºC for A. floridanus, about 11ºC for E. oplophoroides, about 9ºC for A. pouang, L. parvulus, P. guyanae., P. guyanae and P. hemphilli, and P. profunda and about 8ºC for A. puapeba and M. americana. It is further suggested that the shoreward boundaries of some of the subtropical species are set by maximum summer temperatures critical for their survival: about 20-22ºC for A. puapzba and about 17-18ºC for A. pouang and M. americana.
