Ever since Marine Ecology began to take its place as a section of Biological Research, divergent views have been held as to the limits of marine and supra-marine regions; particularly is this so with regard to the fixation of the boundary between littoral and sub-littoral regions. Thus Murray(1898) defines littoral as down to 20 fathoms, while Flattely and Walton(1922) in their devision of plant zones, consider this lower boundary to be at low-water mark. Sernander(1927) applies the degree and nature of exposure as a principle of division. On his principle the boundary between littoral and sub-littoral would coincide with the lower limit of intermittent exposure.