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Multivariate statistical procedures are used to distinguish species in the reef-coral genus Stephanocoenia through a continuous Neogene sequence (five-million year time interval) in the Cibao Valley of the northern Dominican Republic. This genus is the only member of the family Astrocoeniidae that occurs in the sequence. The material consists of 56 colonies (17 of which are measured) from 24 localities in four river sections, the most important being Rio Gurabo and Rio Cana. Ten characters are measured on each of 10 corallites per colony. The data are analyzed using cluster and canonical discriminant analysis to group colonies into clusters representing species. Identical measurements on modem colonies collected near Discovery Bay, Jamaica are included for comparison. Two fossil species are defined in the analysis, one of which is new (Stephanocoenia duncani, n. sp.). Both species are significantly distinct from the single modem species (S. intersepla) that is the sole living representative of the genus. Study of collections from other reef localities shows that both fossil species occur only during Neogene time and only at a limited number of localities. Patterns within each species are traced up a composite stratigraphic section using nonparametric statistical analyses. One of the two fossil species (S. spongiformis) is found to remain stable through time, whereas the other (S. duncam) changes its morphology in a direction approaching the cluster for the modem species. Further study of patterns of variation within the one modern and two fossil clusters shows that intraspecific variation is unusually complicated in this genus. The clusters overlap, and colonies within each cluster differ widely. Variation between populations within the modem species occurs in the same characters as those which distinguish the modem species from the fossil species converging with it (S. duncam). However, these two species form a morphologic continuum that cannot be explained by environment alone. Therefore, they may represent two gradually intergrading chronospecies within one lineage. Of the two fossil species of Stephanocoenia defined, one species (s. spongiformis) exhibits an evolutionary pattem similar to that observed in the family Poritidae. In this pattern, species were found to have short durations and stable morphologies and to have become extinct during the mid- to late Pliocene through early Pleistocene mass extinction. In contrast, the second species of Slephanocaenia (S. duncam) may have evolved over a long time period, possibly forming chronospecies that survived the mass extinction. Unlike genera in the Poritidae, however, no radiation of taxa occurred in the genus after the extinction event. Since no consistent relationship has been discovered between morphology and environment in these corals with the data at hand, their paleoecologic value can only be determined after data on more taxa are collected, and their associations with other corals are studied. This study represents part of a multidisciplinary project on the stratigraphy and paleontology of the northern Dominican Republic, coordinated by P. Jung and J. B. Saunders of the Naturhistorisches Museum Basel, Switzerland.