Until the beginning of this century Colpomenia sinuosa (Mert.) Roth was the only species of the genus known in European waters; it was first found by Mertens in 1806 off Cadiz. Mertens made drawings of it and sent them with his specimens to Roth who described it as Ulva sinuosa and published the description of this alga and Mertens’ drawings in his Catalecta Botanica vol. III in that year. At the beginning of this century a Colpomenia caused considerable damage to the oyster industry in France. Plants of Colpomenia attached themselves to the oysters in the oyster beds at Vannes and other places on the west coast of France. When the Colpomenia bladders became old they were filled with a mixture of air and water and caused the oysters to be buoyed up to the surface of the water and float away and be lost. This Colpomenia spread to the Channel coast of Brittany and Normandy and across to the Scilly Isles and along the south coast of England and became well established there early in the century.