SUMMARY The Ria de Arosa is a large inlet of the Atlantic in western Galicia, NW Spain. It is little influenced by river discharge, the salinity is therefore the normal one for sea water, 33-36°/oo. According to Cadée (1968) the rocks exposed on the coast are for for the greater part granites; the rest, especially on the northwestern and northern coast, being gneisses and micaschists. Seven foraminiferal facies could be made. The L/D ratio is extremely low. It varies from zero to 18.5; the medium ratio is 2.3. Transport of shells from the continental shelf into the bay is rather high and more or less confined to the outer bayzone. The Recent foraminiferal fauna of the Arosa Bay has a fairly large number of species in common with the littoral Pliocene and the oldest littoral Pleistocene of the North Sea Basin. On the other hand the Recent and Holocene faunae of the North Sea Basin show hardly any resemblance with that of the Ria de Arosa, nor with that of the Mediterranean. 193 species of Foraminifera were found, of which 3 were new. The areal distribution of 15 species has been plotted on maps. INTRODUCTION The present study forms part of a biological, oceanographical and sedimentological investigation carried out in the Ria de Arosa, northwestern Spain, 1962-1964. The present paper deals with the Foraminifera collected during these investigations. A representative collection of all species of Foraminifera obtained in the Arosa Bay is kept in the Rijksmuseum van Natuurlijke Historie, Leiden, Netherlands and in the Rijks Geologische Dienst, Haarlem, Netherlands.