Named after the Norse river through which dead must pass.
A sulcus is an are subparallel furrows and ridges. On Triton they are named after aquatic names, excluding Roman and Greek. Possible categories include worldwide aquatic spirits, terrestrial fountains or fountain locations, terrestrial aquatic features, terrestrial geysers or geyser locations, terrestrial islands.
Sorry, there hasn't been a good map made for this world yet :(