The late Devonian—Carboniferous (D–C) shark Thrinacodus has been known only from highly distinctive teeth since its first description from North America in 1875. The poor quality of illustrations of the type material meant that the thrinacodont tooth form remained unrecognized until the early 1980s when similar teeth were found in D–C boundary beds in Australia. Since then, Thrinacodus taxa have been found globally with a Paleotethyan distribution. Discovery of articulated specimens in the Serpukhovian of Montana could have helped to clarify their phylogenetic relationships and paleobiology of Thrinacodus, but their first formal description has caused taxonomic confusion rather than resolving problems of the thrinacodont taxonomy. A new genus, Thrinacoselache Grogan and Lund, 2008, was mistakenly erected, the introduction of which is rectified here and supported by taxonomic arguments. A new interpretation of the phylogeny of Thrinacodus is proposed.