1. A diving helmet can be used successfully on British coasts.
2. An ecological survey, extending to a depth of 10 feet below low water of ordinary spring tides, has been made of a small area in Wembury Bay, S. Devon.
3. Below low water of ordinary spring tides upward facing rock surfaces were occupied by a “Laminaria forest association.”
4. Below L.W.O.S.T. vertical or overhanging rock surfaces were occupied by a “Distomus-Halichondria association.”
5. Large brown Algæ are excluded from the Distomus-Halichondria association by some factor connected with the slope of the rock surface, other than inadequate illumination.
6. Freedom from silt deposition may be responsible for many of the peculiarities of the Distomus-Halichondria association,—in particular for the importance of sponges, cœlenterates, and tunicates.
7. Barnacles play an important part in the recolonisation of bare rock surfaces.