A key to species groups of the genus <i>Belostoma</i> Latreille, 1807, using new taxonomic characters are presented as well as the revision of the four species included in the <i>denticolle</i> group: <i>B. denticolle</i> Montandon, 1903, and three new species: <i>B. orbiculatum</i> from eastern Argentina and southern Brazil, <i>B. retusum</i> from eastern Argentina and <i>B. amazonum</i> from northern Brazil which are described and illustrated.Facultad de Ciencias Naturales y Museo