Twenty-one additional species new or rare to Nova Scotia are reported. Of these, 12 belong to the Rhodophyceae, 6 to the Phaeophyceae, 1 to the Chlorophyceae, and 2 to the Xanthophyceae.Acrochaetium porphyraeandScytosiphon dotyi, two species previously known only from the west coast of North America, are recorded for the first time from the Atlantic coast of that continent.Porphyrodiscus simulonsandEntonema polycladum, known from Europe, are also recorded for the first time in North America.