Helodus (from Greek: ἧλος helos, 'stud' and Greek: ὀδούς odoús 'tooth') is an extinct genus of cartilaginous fish from the Upper Devonian through Lower Permian. While the type species, H. simplex from the Late Carboniferous (Moscovian ~ 315 million years ago) of England is known from articulated specimens, the rest of the species in this genus are known only from isolated teeth. Over seventy species have been attributed to this genus, many of which may be anterior teeth of other cartilaginous fish. This makes Helodus a wastebasket taxon. Only the type species can be confidently attributed to this genus until articulated remains of other species are found. H. simplex was around 30 centimeters (1 foot) long, and males had a large, tooth-bearing clasping organ on their heads. The teeth of H. simplex, which were arranged in tooth-whorls, were transitional between elasmobranch-like separated teeth and the tooth plates of living chimaeras.