Parastylonurus is a genus of prehistoric eurypterid. It is the only genus classified in the family Parastylonuridae and contains two species, P. hendersoni and P. ornatus from the Silurian of Scotland.

Parastylonurus was a stylonuroid of small to medium size with a rounded prosoma wider than it was long. The eyes were located on the anterior half of the carapace and the metasoma was very long. The first three walking legs were very short with single opposable spines on every joint. The last two walking legs were very long, reaching to the last tergite. The opisthosoma was narrow and undifferentiated and the telson was spike-like.

Parastylonurus can be differentiated from the closely related Stylonurus in that it lacks the distinct trilobation present in Stylonurus and by the position of the eyes.

Parastylonurus contains two valid species, with other named species now seen as invalid or as part of other genera.

Invalid or reassigned species are listed below: