In 1890, Traquair assigned isolated fin spines from the Early Devonian of eastern Canada to a new gyracanthid acanthodian Gyracanthus incurvus, based on the similarity of the distinctive oblique ridges on the spines to the ornament on the large robust fin spines of Gyracanthus spp. from the British Carboniferous Coal Measures. Other similarly ornamented spines from the Early Devonian of Germany were tentatively assigned in 1933 by Gross to the same genus as a new species Gyracanthus? convexus. Based on examination of the type material, as well as newly collected specimens from Emsian sandstones and mudstones of the Gaspé Peninsula, Quebec and the Atholville beds, New Brunswick, we erect a new genus Ankylacanthus gen. nov. for these two species. Spines of the new genus are distinguished by being laterally flattened and thin-walled, with a single row of denticles along one side of the posterior groove, and having thin spine ridges ornamented with low smooth nodes. Other Early to Middle Devonian specimens in South America, Saudi Arabia, and Iran are also tentatively referred to the new genus, which seems to have had an early (Lochkovian–Pragian) cross-north Gondwanan distribution, transferring into Laurentia and spanning Emsian–Eifelian times.