AbstractThe differences betweenThysanomitriumSchwaegr. andCampylopusBrid. are discussed and regarded as insignificant. Therefore the sixThysanomitriumspecies reported from South America in theIndex Muscorumare critically revised.T. yunqueanumC. Müll. andT. miserumBroth. are synonyms ofCampylopus richardiiBrid., andT. schiffneriBroth. andT. arenaceumBroth. are placed in the genusCampylopusas new combinations. AlsoT. arenaceumis reported from a new locality in Brazil. No material could be found in herbaria ofT. wainoiBroth. andT. gastrotisC. Müll.