Thorius infernalis (common name: Atoyac minute salamander) is a species of salamander in the family Plethodontidae. It is endemic to Mexico where it is only known from its type locality in the Sierra Madre del Sur in central Guerrero. Its natural habitat is riparian vegetation along hillsides, presumably in forest. It is only known from two specimens, and it has not been seen since early 1980's. Much of the potential habitat is already converted into coffee plantations. It is threatened by habitat loss caused by expanding agriculture and human settlements.