Foraminifera were abundant in samples obtained from the Mauritanian coast. Their ecology and geographical location was studied. The genera and species are initially grouped according to the nature of the seabed and its depth. Those found in (1) deep mud at 500-1200 m, (2) muddy sand at 20-340 m, (3) shelly sand at 30-52 m are considered in turn. Group (I) varied according to the station of collection, and were affected by factors in addition to depth, such as the presence of corals. Muddy sand was poor in large individuals and in empty shells, but contained many displaced littoral forms. The very few living forms found in the shelly sand area was surprising; it may reflect the constant agitation of the sand or the small size of individuals, which could have slipped through the washing filter. Foraminifera fall into 2 broad categories, one large, arenaceous and adapted to depths, the other small, calcareous and littoral.