Algal limestones in the coal-bearing upper part of the Pennsylvanian Morien Group in the Sydney Basin, Nova Scotia, contain abundant fish fragments. A wide variety is present, including remains of bony fish, lungfish, and sharks. Of these, the most significant environmentally are the lungfish and the teeth and skeletal fragments from freshwater xenacanthid sharks. Their presence confirms the earlier diagnosis of nonmarine conditions derived from the nature of the sedimentary succession and the other biota present. Lithologic and faunal associations suggest that the xenacanthid sharks lived mainly in shallow, alga-bearing lakes on alluvial plains, whereas the bony fish were also tolerant of more restricted swampy environments marginal to the lakes.