A population of the Early Devonian brachiopod Discomyorthis musculosa, from Quebec, Canada, was preyed upon by a boring carnivore, possibly a gastropod. The predator preferentially attacked this species and selected a specific size range of prey. Large size seems to have provided a refuge from predation. Predation was a significant contribution to mortality during part of the life history of the population. Examination of survivorship curves reveals the number of individuals which would have lived through the interval of predation was reduced by more than 50% because of predation. This may be an early Phanerozoic example of diversity regulation by predation.