Certain zones of the massive grey dolomite belonging to the Niagara Formation in North America are so largely composed of fossil corals as to indicate similar conditions of formation to that of the coral reefs of the present age. Perhaps no better examples of these Palæozoic coral reefs could be found than those which are exposed in many tracts of the surface of the Great Manitoulin Island, which are literally covered with complete and fragmentary corals in a silicified condition, which have been weathered out of the matrix of hard dolomite in which they had been imbedded. The great majority of these corals belong to the well-known genera Favosites, Halysites, Heliolites, Alveolites, Cænites, Syringopora, Strombodes, Cyathophyllum, Zaphrentisand Omphyma, and many of the species are also common to the Silurian rocks of Europe. A recent search in the dèbris of one of these ancient reefs has brought to light a coral which appears to belong to a new genus, with the following characters.