Two new tetraphyllidean cestodes are described from the freshwater stingray Potamotrygon magdalenae from Colombia. The new genus Potamotrygonocestus is proposed for P. magdalenensis, which differs from Pedibothrium by having a bilobed rather than X-shaped ovary, and simple rather than bifid hooks. It further differs from Pachybothrium hutsoni by having bothridial hooks inserted immediately posterior to an accessory sucker rather than inserted in the middle of a thick muscular pad. Potamotrygonocestus magdalenensis is unique among known tetraphyllideans by possessing vitellaria which are compact, cylindrical bands in the lateral portions of the middle of the proglottid. The second new species, Rhinebothrium moralarai, resembles R. scorzai by having its genital pore and terminal genitalia at the ovarian level, greatly reduced poral ovarian lobes, and by parasitizing a freshwater stingray. It differs from R. scorzai in number of bothridial loculi, testes per proglottid, and proglottids per strobila; by having quadrate rather than canoe-shaped bothridia; and by parasitizing Potamotrygon magdalenae rather than P. hystrix.