Tremiorchis ranarum nov.gen., nov.sp., was first found in the small intestine and duodenum of thirty-six out of one hundred and two specimens of Rana tigrina examined for the purpose. Subsequently many more frogs have been examined and we have obtained these parasites in one out of every three frogs. Rana tigrina being the commonest species of frog available in Northern India is used as the type for dissection in every laboratory and it appears, therefore, strange that this common Trematode parasite should have remained unknown till now. The number of parasites in a host is very variable. Three hosts were found infected with one parasite each, one had 4, one had 5, one 16, one 18, one 196 and one as many as 204.