This paper revises the genus Stenostomum based on a rich collection of species from Argentina and on a review of bibliographical resources of all known South American species. The description of South American species is standardized. The new genus Anokkostenostomum is established and several species of Stenostomum are transferred to it based on the absence of light-refracting bodies and the presence of a metameric anterior brain lobe. We report five Stenostomum species and three Anokkostenostomum species new to Argentina and present an identification key for South American species. Finally, all the world species are compiled, with an overview of their distribution.Facultad de Ciencias Naturales y Muse
