Keys are given to the genera of the Microascaceae and to the species of Petriellidium and Pithoascus. In Petriellidium six species are accepted, P. desertorum, P. ellipsoideum, P. fusoideum, and P. africanum are described as new. In Pithoascus also six species are enumerated, P. platysporus and P. stoveri are described as new, for Microascus exsertus Skou the combination Pithoascus exsertus is proposed.