Included in a large assemblage of corals from the Lower Carboniferous Shales—referred to a Z horizon—overlying the Lower Carboniferous Sandstone anticline (K) on the north coast of Co. Sligo is a remarkable new genus—Caenophyllum—which forms the subject of this paper. Caenophyllum gen. nov. claims distinction in showing a very unusual life-history—quite unlike that of any known coral; and forms a very interesting example of abnormal coral ontogeny. The shales form cliffs at Pollarone, near Dromore West, Co. Sligo, and vary in height from 30 to 50 feet. They are cut off by the rising tide, and consequently have hitherto been neglected; but are of great importance in zonal work, as they contain a rich coral and Bryozoan fauna and thus form a starting point for zonal investigation.