A new species of freshwater crab of the genus Microthelphusa Pretzmann, 1968, from Guyana, South America is described. Microthelphusa meansi, new species, was collected from a remote isolated cloud forest in the Wokomung Massif, a tabletop mountain (tepui) in western Guyana at over 1,000 m above sea level. The conspicuous horseshoe-like marginal lobe and the dome-like auxiliar cephalic lobe of the first gonopod clearly distinguish this species from all 12 congeners.