Praearcturus
Praearcturus is an extinct genus of scorpion known from the late Devonian of what is now Britain. It is the only genus in the family Praearcturidae and contains the single species Praearcturus gigas. The type fossil was discovered in Rowlestone, England, and was described in 1871 by Henry Woodward. The species could reach a total length of nearly , making it one of the largest scorpions known. References 

Prehistoric scorpions

Devonian arachnids
Fossil taxa described in 1871