Helodus
Helodus is an extinct genus of cartilaginous fish from the Upper Devonian through Lower Permian. While the type species, H. simplex from the Late Carboniferous 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 as broadly defined 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 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.