: The subgenus Rhysoceratina of Ceratina is restricted to South America, with known species in Argentina, Brazil, Colombia, Paraguay, and Uruguay. Nine species are recognized, four of which are described as new: C. canaliculata, C. pusilla, C. mendozina, and C. nitidifrons . Lectotypes are designated for C. catamarcensis Schrottky, 1907, and C. volitans Schrottky, 1907. A phylogenetic analysis supports the monophyly of the subgenus and, within it, of two major species groups. A key to the species, descriptions, distributional data, and illustrations are provided.