Morphologically the fungus reminds one of the Microsporum species of man. The microscopic elements are: the shape of the mycelia within the hairs, size and disposition of spores intercalar and terminal chlamydospores, simple clusters, hyphae, pectinate and denticulate elements. Of the 17 species of Microsporum described up to now, none can be identified with Microsporum circuluscentrum. The microsporum described is of the pure-by human type. (Culture fairly vivacious, almost total absence of spindles.) Microscopically at first sight the culture might be taken for Microsporum fulvum URIBURU 1917 or for M. felineum. These are however from animals. The bean shaped culture on potatoes leaves a place apart for it among Microsporum fungi. The anomalous elements seen in the cultures are also found in other species of Microsporum. Besides the pseudo-perithecia described and interpreted I must mention that the pseudo-nodular organs are not an exception among these fungi, for Microsporum fulvum also shows what writers have described as nodular organs. The spiral elements are also not exclusive features of the trichophytes. Microsporum tardum also shows quite characteristic spiral forms.