''Procephalaspis'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus of

jawless fish Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfish ...

References

* Telling the Evolutionary Time: Molecular Clocks and the Fossil Record (Systematics Association Special Volume) by Philip C J Donoghue and M. Paul Smith (page 227) Osteostraci genera Silurian jawless fish {{Paleo-jawless-fish-stub