The material on which the present paper is based was collected in fresh- and brackish-water habitats on the islands of the Leeward Group, West Indies, in 1936 and 1937. For completeness sake specimens from brackish water and from some isolated salt-water habitats — already studied by the author (K. STEPHENSEN, 1933a and 1933b) — were included. It seems highly probable that the greater part of the species treated below are also represented in the litoral fauna of the open sea. The occurrence of the species on the various islands may be summarized as follows (see also Table 1.)