Among the shore crabs the genus Callianassa is quite cosmopolitan; its species are widely distributed and seem also to be peculiarly susceptible to parasitism. Wherever they have been examined carefully they have yielded semi-parasitic copepods, sometimes in considerable numbers. Such forms have been reported from both the east and west coast of North America, from the Mediterranean and from the British Isles. Recently 150 of these semi-parasites were sent to the United States National Museum from Salaverry near Trujillo on the coast of northern Peru. They were taken by Mr Floyd Sears, agent of the Grace Line at Salaverry, from the branchial chamber of a species of Callianassa on the Peruvian coast. They prove to be new species belonging to two genera of cyclopid copepods and are here described and figured.