Ultrastructural and morphological studies have been carried out on M. tumidum, the type species of Myelosperma. Asci are provided with a distinctive refractive subapical ring, which differs from that found in other unitunicate families. The ascospores are reniform in all species and surrounded by mucilaginous sheaths of various shapes. Numerous ascomata also develop in a circle around a common central pore. At the ultrastructural level the ascus apex comprises an electron-transparent thickening incorporating a subapical electron-dense hemispherical ring-like structure and the ascus wall is continuous over the apex. This type of ring is compared with those found in representative species in other related families. Based on these observations, a new family, the Myelospermaceae, is introduced, to accommodate Myelosperma. The rationale behind this is discussed, and M. alata is described to accommodate a remarkable new species from the Seychelles. Arguments for the possible inclusion of Manokwaria, Palmicola and Pemphidium in the Myelospermaceae are given.