Abstract
The life history of Z. rubellus was traced; D. lasium and C. lintoni are identified as its cercarial stage. The metacercaria occurs in Nereis virens, the adult stage in marine fishes. The successive stages in the life cycle and the development in each host are described. Previous accounts of the species are discussed. The larval trematodes included in the group Cercariaeum are shown to be a heterogeneous assemblage. Since the group has no genetic entity, the name Cercariaeum is suppressed and the spp. are referred to the larval group Cercaria.