The adults of tapeworms, the plerocercoid larvae of which caused epizootics in trout in reservoirs near Dublin, and also in S. Wales, are believed to represent 2 spp. of Diphyllobothrium, one parasitic in gulls, the other in cormorants. The gull tapeworm is D. dendriticum; specimens reared in mammals showed slight differences, probably due to development in an abnormal host. The tapeworm of cormorants is not named.