What is "phlegethontia"

Phlegethontia is an extinct genus of lepospondyl amphibian from the Carboniferous and Permian periods of Europe and North America. Phlegethontia was an aïstopod, a group of legless, burrowing, snake-like amphibians. It was about long, and possessed a lightly built skull with many openings, unlike some earlier relatives.

"Dolichosoma" longissima, named by Antonin Fritsch in 1875, has been reassigned to the genus Phlegethontia and is now considered to be P. longissima. "Dolichosoma" has been considered to be a nomen nudum because the holotype was inadequately described through a layer of matrix by Thomas Henry Huxley in 1867.