Termitarla snyderi Thaxter is an entomophilous fungus growing on the exoskeleton of different species of termites. The fungus is an ectoparasite. Specialized thick-walled haustorial mother cells of the basal layer of the fungal sporodochium send haustoria into the integument of the host. The haustorial peg enters the host through the pore canals of the host cuticle. The haustoria are lobed, uninucleate, surrounded by a thick wall and separated from the host protoplast by its plasma membrane. Along with usual organelles the haustoria contain certain vacuoles that are lysosomal in nature, and a new organelle, mini-microtubules o that are only 80 to 100 A in diameter and have six sub-units. The mini-microtubules are found in bundles free in the general cytoplasm, between the cisternae of smooth endoplasmic reticulum, between ER ci sterna and plasma membrane or between ER ci sterna and the nuclear envelope. The only known means of reproduction is the formation of conidia that are cut off endogenously by the phial ides at the VI conidiogenous loci into long collarettes in basipetal succession. Phialides are closely clustered into a sporodochium. The conidia are catenate, cylindrical, uninucleate and hyaline. It is proposed here that the conidia germinate to form a crust-like primary thallus that later, by the development of phialides over it, matures into a sporodochium. The taxonomic position of Termitaria and its relationship with other imperfect fungi are discussed. Within the fungi imperfecti a new family and a new order, Termitariaceae and Termitariales respectively, are proposed to accommodate Termitavia and Mattirolalla. A new species of Mattirotella based on the slide of Termitaria made by Thaxter is also described.