As a result of recent investigations1 into the distribution of the Radiolaria in the sediments collected by the Swedish Deep-Sea Expedition in the Western Pacific Ocean, two conclusions of outstanding importance can be drawn: first, that several species of Radiolaria which are widely distributed in the tropical oceans of the present day do not extend farther back in time than the very latest Tertiary or early Quaternary; secondly, that erosion and re-distribution of older sediments on the deep-sea floor often result in the mixing of the tests of Tertiary Radiolaria with Recent ones in that region.