The author found 15 communities distinctive of the different types of habitat, e.g., rock, sandy mud-covered rock, pebbles, sand and pools. The Porphyra-Urospora-Ulothrix community, the Laurencia-Lomentaria community, the Laurencia-Cladophora-Rhodochorton community and Enteromorpha-Cladophora-Chordaria community have not been previously recognized. The communities described are all perennial except, the Porphyra-Urospora-Ulothrix community and the Enteromorpha-Cladophora-Chordaria community, the former occuring only in winter and spring and the latter in spring and summer. Many of the perennial communities, however, include so many annual and short-lived spp. that the composition of any community is usually undergoing changes. This is best illustrated in the case of the Laurencia-Lomentaria community. The communities which exhibit least seasonal change are (1) the Laminaria community, and (2) the community hanging under ledges, the composition of which remained remarkably constant throughout the year. The horizontal distribution of the vegetation in the area is chiefly influenced by the degree of exposure to wave action. The vegetation in the southern, more exposed, part of the area differs noticeably from the northern, more sheltered, part. Several communities are restricted to the southern part, e.g., the Himanthalia community, the Laurencia-Lomentaria community and the Porphyra-Urospora-Ulothrix community, while those occurring on movable substrata such as sand or pebbles are confined to the most sheltered northern part. The effect of exposure is also very marked in the size and development of spp. of Fucaceae, such as Ascophyllum and Fucus vesiculosus, which occur throughout the whole area. Owing to the large tidal range and gentle slope many of the communities cover large areas of shore. In the north of the area the slope is gentlest and such communities as the Enteromorpha community, the sublittoral community on pebbles and the Laminaria community occupy very large intertidal areas strewn with sand, pebbles and boulders. In these gently sloping places the boundaries of the communities are not nearly so clearly defined as on the steeper ground towards the south.