It was stated in the second paper of this series that the disposition of the Lecideaceae in an early paper of the series would show what slight changes are needed in treating lichens as we treat other ascomycetes. It is hoped that this paper has accomplished this in phraseology intelligible to those acquainted with the present-day language of systematic mycology. The Lecideaceae form a well-defined family of lichens, the affinities of which seem plainly marked. In apothecial structure, and so far as known, in structure of the sexual reproductive areas, the family seems to be closely related to the mainly non-lichen Patellariaceae and to such lichens as the Gyalectaceae, the Lecanactidaceae, the Collemaceae, the Baeomycetaceae, and the Cladoniaceae.