Language: English
Family Percichthyidae, Subfamily Percichthyinae and its genera Percichthys and Santosius n. gen. are diagnosed. Percichthys trucha, Percichthys hondoensis, Percichthys lonquimayiensis, Percichthys sandovali n. sp., and Percichthys melanops are included in the genus Percichthys; all of these species are described. Guayquichthys ferugloi Dolgopol is considered as synonym of Percichthys hondoensis. The Family Perciliidae is diagnosed, and Percilia gillissi and Percilia irwini are redescribed. The Family Percichthyidae is represented in the fossil record by Percichthys hondoensis in the Eocene of Argentina, by Percichthys lonquimayiensis and Percichthys sandovali n. sp. in the Upper Paleocene of Chile; and by Santosius antiquus in the Upper Tertiary of Brazil. Even in the Tertiary, the freshwater percichthyids were distributed in Brazil and southern South America, actually they are restricted to the South of Chile and Argentina.
A comparison between South American members of Percichthyidae, Perciliidae and some serranids is made, and some diagnostic characters are discussed.