SUMMARYAlthough earlier North American records ofStictyosiphon soriferus(Reinke) Rosenvinge cannot he substantiated, the species is shown to be common in Newfoundland and is also reported from Nova Scotia. Plants are summer annuals and a component of ephemeral subtidal communities characteristic of suitable inlets and harbors. Only plurilocular reproductive organs are produced. In culture the life history of populations from both sides of the North Atlantic consists of a direct replication by asexual zoospores. A microscopic stage might occur in the field, and is presently known only from European cultures. In eastern CanadaS. soriferusis readily distinguishable fromS. tortilis(Rupr.) Reinke,S. subsimplexHolden andS. griffithsianus(Le Jol.) Holmes&Batters.