Stylonurus is a genus of prehistoric eurypterid of the family Stylonuridae. The genus contains three species: Stylonurus powriensis from the Devonian of Scotland, Stylonurus shaffneri from the Devonian of Pennsylvania and Stylonurus perspicillum from the Devonian of Germany. The assignment of S. perspicillum and S. shaffneri to the genus is doubtful. A previously assigned species, S. ensiformis, is today regarded as synonymous with S. powriensis.