Synsphyronus callus is a species of pseudoscorpion in the Garypidae family. It is endemic to Australia. It was described in 1947 by American arachnologist Clarence Clayton Hoff.[1]
The body length of the holotype female is 3.3 mm. The colour is brown.
The species occurs in south-west Western Australia in rocky coastal habitats. The type locality is Rottnest Island, with a paratype specimen obtained at Cottesloe Beach near Perth.[1]
The pseudoscorpions are terrestrial predators.[1]