A comparative ontogenetic study was initiated on three genera of coprophilous discomycetes ; Thelebolus, Lasiobolus, and Thecotheus . These organisms were chosen because they represented fungi that possess different numbers of asci and ascospores per apothecium. These genera have been placed at one time or another in the family Thelebolaceae, The variability of characteristics for these three genera and others previously reported seems to indicate that the familial limits of Thelebolaceae should be much more restricted. Thelebolus stercoreus shows an ascocarp ontogeny similar to Trichobolus zukalii . The mycelium of T. stercoreus is uninucleate. Ascogonial initiation begins with an evagination from a parent hypha. No croziers are formed as the single ascus grows directly from a privileged cell of the ascogonial coil. Nuclear divisions in the ascus have been followed and photographed, Thelebolus stercoreus represents perhaps the highest evolutionary form found in the coprophilous habitat. Its unique structures must limit the family Thelebolaceae to Thelebolus, Trichobolus and perhaps Ascozonus and Caccobius, The latter two genera need further study before a familial alliance can be established. The ontogeny of Lasiobolus ciliatus begins with an evagination from a parent hypha that develops into a multicellular stalked ascogonium, Hyphae from cells below the ascogonium and from surrounding hyphae ensheath the ascogonium. This development is similar to that shown for Cheilymenia stercorea, Scutellinia scutellata and Coprobia granulata, Ascogenous hyphal growth is terminated by the development of croziers (pleurorhynque), In the present study ascal cytology has been described and photographed. The mycelium of L. ciliatus is uninucleate. The development of the diagnostic hairs of Lasiobolus is presented. The study of ascocarp ontogeny was facilitated with plastic embedding. It is suggested that Lasiobolus has familial affinities with the Aleuriaceae. Ontogenetic features of Thecotheus were investigated using two species, Thecotheus cinereus, an eight-spored species and Thecotheus pelletieri, a 32-spored species. The ascogenous system of Thecotheus consists of a series of ascogonial cells similar to that of Ascobolus citrinus . The ascogonia give rise to ascogenous hyphae that terminate with the formation of croziers (pleurorhynque) . The mycelium of both species is mostly multinucleate. Both species also produce "primordial humps" that consist of bulbous cells that resemble the microconidia of Ascobolus carbonarius . This stage precedes ascocarp initiation, and they appear to only function in excipular formation. A sympodial imperfect stage of T. pelletieri is described and photographed. Sympodial conidia have also been described for the Aleuriaceae. It is thought until more information is available for Thecotheus and other genera, especially in the Aleuriaceae, the best placement is in the lodophaneae of the Ascobolaceae.