Phlysacium Hawle et Corda, 1847 Rejkocephalus Kordule, 1990 Hydrocephalus ("water head") is an extinct genus of redlichiid trilobite that was very common during the Middle Cambrian of Eurasia and North America, which lasted from 508 to 497 million years ago.

This trilobite is up to 20 cm long and more widely built than others of the time.

In comparison to other members of its family, its glabella appears swollen.

Data related to Hydrocephalus at Wikispecies

This Redlichiida-related article is a stub.