After studying more than thousand Spirobranchus worms from Curaçao and other Caribbean Islands, and after comparison with the material from other tropical and subtropical regions, it appeared that in the West Indies 3 species and 1 variety of Spirobranchus could be recognized; viz: Sp. giganteus giganteus: large (45—66 mm), more or less solitary; operculum with 2 or 3 antler-like horns; branchiae in a spiral. Sp. tetraceros: smaller (30—40 mm), more or less gregarious; operculum as a rule with 3 groups of much branched horns, appearing as 6 or 8 distinct horns; branchiae not in a spiral. Sp. polycerus: small (about 15 mm), usually forming colonies; operculum in general with 7 small horns, sometimes small secondary spines; branchiae in a spiral. Sp. polycerus var. augeneri n. var.: small (about 14 mm), usually colonial; operculum with 2 ox-horn shaped horns, also a medio dorsal knob may be present; branchiae in a spiral. The material studied was mainly collected by Dr. P. WAGENAAR HUMMELINCK (1930, 1948—49, 1955, 1963—64, 1967), when sampling a number of habitats in the tidal zone and below, to a depth of about 2 m. The material, as a rule, has been preserved with formaldehyde, and was, after a short period, transferred to alcohol. The specimens studied are mainly in the author’s collection or in the Rijksmuseum van Natuurlijke Historie, Leiden (nrs. 04400—04429, 04431); small, but representative series are in the Zoological Musea of Amsterdam, Utrecht, Copenhagen, Hamburg and Jerusalem.