Brachiopods belonging toAmbocoeliaoccur ubiquitously in Middle and Upper Devonian strata of the northern Appalachian Basin. Originating during the Eifelian,Ambocoelia umbonatapersisted through numerous biocrises, but went extinct during the late Frasnian Kellwasser Crisis.Ambocoelia umbonatavar.gregaria, the only other form of this genus that is present within the New York Devonian succession, originated around the time of the Kellwasser Crisis and persisted locally into at least the latest Famennian. Examination of syntypic material ofA. umbonatavar.gregariahas resulted in the taxonomic revision of this form and elevation toAmbocoelia gregaria. Comparison of ontogenetic stages and environmental preferences ofA. umbonataandA. gregariasuggests that the latter exhibits a paedomorphic morphology that may have evolved fromA. umbonatathrough neoteny. Furthermore, these comparisons also give new autecological insights forAmbocoelia, suggesting thatA. umbonatawas capable of living in a diversity of environments by using a variety of life positions, whereasA. gregariawas likely more specialized. This taxonomic revision provides the necessary framework for revising the biostratigraphic range ofAmbocoeliaand, furthermore, the evolutionary history of this genus in relation to the Lower Kellwasser Event.