-3- studied and reported on by Taylor (1950), Fosberg (1953), St. John (1949), and Biddulph (1952). Dawson (1957) has reported on the algae of Eniwetok Atoll. Studies on the distribution of radioactive materials produced by the atomic tests conducted in the Marshall Islands have been published by the Laboratory of Radiation Biology, * University of Washington, as research and development reports for the U. 8S. Atomic Energy Commission. An atoll may be described as a roughly oval, coralline reef rising 15, 000 feet above the ocean floor. Within the surrounding reef there is enclosed a shallow lagoon generally with a maximum depth of about 180 feet. The lagoon is open to the ocean by one or more passes cutting through the reef, most of which is awash except at low tides. Emergent land consists of low sandy islands with an elevation seven to ten feet above sea level; elevations as high as twenty feet are rare. occupy only a small fraction of the total area of an atoll. The islands Bikini lagoon covers 229 square miles (Handbook on the Trust Territory of the Pacific Islands) and has a dry-land area of two and a third square miles divided among some thirty-six islands and islets; Eniwetok lagoon covers 388 square miles, has a dry~land area of two and one-fourth square miles, and forty islands. These atolls lie in a zone of the northeast trade winds. Because of the constancy of direction of the winds, there are distinct differences in reef form between the windward and leeward sides of the atoll. The wind- ward side is generally considered the region of most rapid growth and is *Formerly the Applied Fisheries Laboratory >