SUMMARY1A quantitative investigation of the marine bottom fauna has been earned out, in conjunction with an analysis of the physical environment, across the continental shelf off Accra from the shore to a depth of fifty fathoms.2The concept of “community” used in the present work is discussed and defined.3Although the nature of the bottom sediment is of primary importance, wave action in shallow water and temperature in deeper water are important factors in community differentiation.4Four distinct infaunal communities have been recognised associated with four different types of bottom conditions, these are:(a) The Inshore Fine Sand Community (0 to eight fathoms), dominated by the polychaetesOwenia fusiformisandDiopaira nea/polilanawith the lamellibranchCultellus tenuis.(b) The Sandy Silt Community (8–20 fathoms), withTurritdla annvMaandSternaspis scutata.(c) The Silty Sand Community (20–25 fathoms), dominated by two species of Foraminifera–JullienellajoetidaandSchizamminasp.(d) The Coarse Sand Community (25–50 fathoms), dominated by the coralCaryophyllia clavus.5At depths greater than fifty fathoms a rock epifauna exists which is Mediterranean in nature and contains many new faunal records for West Africa. It is characterised by massive colonies of the coralDendrophyllia rameaand large numbers of the basket starAstrospartus mediterraneus.The bottom temperature at this depth varies little from similar depths in Northwest Africa and the Mediterranean.6The communities off Accra are clear cut and well defined and this is considered to be largely due to the rapidly changing nature of the bottom deposits across the shelf. These rapid changes in bottom conditions are caused first of all, in shallow water, by the sorting action of the surf waves on the bottom deposits. In deeper water a second transition is brought about by the production of coarse sediment from the erosion of a limestone deposit on t