Two subgenera are recognized in Erratencrinurus: E. (Erratencrinurus) and E. (Celtencrinurus) each containing two species groups. A third group of taxa here termed E. (sensu lato) comprises a mid-Caradoc to late Ashgill stock which retains many of the characters of the oldest known species of Erratencrinurus, E. (s.l.) spicatus (Tripp). This species is also closest to the probably ancestral Encrinuroides torulatus-Encrinuroides uncatus line age. Erratencrinurus (Erratencrinurus) inopinatus sp. nov. is described from a newly discovered, unusually diverse fauna in the upper Ashgill ( probably Rawtheyan) Kalvsjø Fm. in the Hadeland district of the Oslo Region.