A new rugose coral fauna from a previously undescribed reef facies of the Coeymans limestone of early Early Devonian age in New York consists of 9 species, all new, assigned to 6 genera, 3 new. Collections are from 9 separate reefs or reef areas in which individual reef-knobs average 100 ft. in diameter and 20 ft. in height. The fauna is peculiar in that most of the species are characterized by partial or complete stereoplasmic filling of the corallum. In this respect it finds a close analogue in the Koneprus limestone of Bohemia (also a reef facies) but the genera in the 2 faunas are not closely related. Two of the species seem to be early representatives of characteristic later genera of Onondaga age, but the phylogenetic relationships of the other species are not clear. Individual variation in 8 of the described species is expressed in standard statistical terms and illustrated by means of scatter diagrams, frequency curves, and average valve curves. In the species studied the septal ratio (number of major septa/diameter) decreases with increasing diameter both among adults and in ontogeny. The tabularium ratio (tabularium diameter/diameter) is constant with increasing diameter among adults but ontogenetically shows a marked decrease with increasing diameter. Variation within colonies of Tryplasma fascicularium is of the same magnitude as variation within populations of solitary cylindrical corals but the conical species show much greater variation.