The moss genus Macrohymenium [Sematophyllaceae] is characterized by a peristome unique among moss genera. The author will present preliminary results of an investigation of this peristome by means of conventional and scanning electron microscopy. The outward similarity of this peristome to that found in the Regmatodontaceae will be discussed. The differences among species of Macrohymenium sensu Eakin will be discussed.

Key words: Macrohymenium, peristome, Sematophyllaceae