In 1969 the author’s attention was caught by the variability of some species of the genus Vermiliopsis, sensu lato, so extreme, that at the time it was impossible to distinguish the various species. The present review is the third in a series of revisionary studies on the former genus Vermiliopsis. The first one dealt with the genus Metavermilia Bush (ZIBROWIUS, 1971), the second with the genus Bathyvermilia Zibrowius (ZIBROWIUS, 1973a). A study on the genus Vermiliopsis, sensu stricto, is in preparation. The material was collected mainly by dr. P. WAGENAAR HUMMELINCK, when sampling on various islands, in a number of habitats from the tidal zone down to a depth of about 2 m (1930, 1948/49, 1955, 1963/64, 1967); by the “Onderzoekingen Continentaal Plat Suriname Expedities” in 1966 and 1969 (shelf of Surinam, 27—130 m); and by the author in 1970 in the Netherlands Antilles (down to a depth of 46 m). This material, as a rule, was preserved with formaldehyde and after a short period transferred to alcohol. These specimens are deposited for the greater part in the Rijksmuseum van Natuurlijke Historie, Leiden (RMNH) or in the author’s collection (tHU). As far as possible, small series have been presented to other museums, which sent material on loan; these are indicated with an exclamation mark in the acknowledgements below.