THE fungus Ophiobolus halimus, which has recently been described as parasitic on Zostera marina L., has this summer been discovered on this plant in the British Isles. It has been found in several localities in Devon (Plymouth, Cawsand, River Yealm, Salcombe), the north coast of Guernsey and Lough Ine, Ireland. Dr. E. J. Butler has compared the British material with authentic specimens of O. halimus, Diehl et Mounce, recently described on Z. marina on the Atlantic coast of North America1, and finds it to be identical with the Canadian material.