Phlegethontioidea
Phlegethontioidea is a clade of aistopod tetrapodomorphss including the families Phlegethontiidae and Pseudophlegethontiidae. It is a stem-based taxon defined in phylogenetic terms as all aistopods sharing a more recent common ancestor with Phlegethontia than Oestocephalus.

References

Aistopods
Carboniferous first appearances
Permian extinctions