1. In this paper, a study of Rotifers has been made of extensive material, collected in the Caribbean province by Dr. P. WAGENAAR HUMMELINCK, between 1930 and 1973. 2. 64 species of Rotifers have been found. For 19 of these, particulars are given on their morphology, ecology and biogeographical distribution. 3. Lecane plesia MYERS 1936 has been redescribed; the taxonomical status of Hexarthra intermedia brasiliensis has been discussed. 4. Three new species have been described: Colurella althausae, Euchlanis perpusilla and Lecane hummelincki. 5. Comments are given on Brachionus calyciflorus with large postero-lateral spines and on a giant form of Tripleuchlanis plicata.