The claim that the Carboniferous chondrichthyan genus Cladodus Agassiz, 1843, is a nomen vanum is critically examined. The teeth of C. mirabilis, the type species of the genus, are re-examined from Agassiz's syntypes and other material. It is concluded that C. mirabilis offers a suite of characters adequate for definition of the genus Cladodus. Comparison of the teeth of Cladodus with those of other Carboniferous shark genera confirms its status as a valid taxon. From this revision it is concluded that C. marginatus, C. vanhornei, C. bellifer, and C. elegans should all be included within Cladodus, while C. striatus Agassiz is placed in the new genus Saivodus. Both Cladodus and Saivodus are considered to belong in the Ctenacanthiformes.