Empruthotrema quindecima sp. n. (Monogcnea: Monocotylidae) is described from the nasal fossae of the blue-spotted fantail ray Taeniura lymma (Forsskâl, 1775) collected from the reef flats of Heron Island and Lizard Island located at the southern and northern sections, respectively, of the Great Barrier Reef in Queensland, Australia. Empruthotrema quindecima has 15 marginal loculi on the haptor which distinguishes it from the other five members of the genus which have either 13 or 14 marginal loculi. The generic diagnosis of Empruthotrema Johnston ct Ticgs, 1922 is amended to accommodate the new species, a key to species is provided and the evolution of the different configurations of the haptoral loculi within the genus is discussed.