The pyrenolichens and their non-lichenized allies are probably the least known group of lichens in North America. Even so, they are as abundant and widely distributed as any other group of lichens. They are inconspicuous and present considerable difficulties, both taxonomic and nomenclatural, but not much more so than most crustose lichens. I began a taxonomic survey of the corticolous pyrenolichens of the Great Lakes region in 1965, and a preliminary report was sumitted as a thesis for the Master’s Degree in late 1966. In the last five years the number of species included has almost doubled, and a number of taxonomic and nomenclatural problems have been resolved. As may be seen from the number of species still unnamed, problems still remain. Further, I anticipate that continued intensive collecting will bring additional species to light. This report should therefore not be considered as final, and is published with the hope of encouraging collection and study of this interesting group of lichens.