Through the kindness of Dr. C. J. VAN DER HORST of Amsterdam, I have had the opportunity of examining and reporting on the collection of ascidians that he made at Curaçao, Dutch West Indies, in April and May, 1920. The collection represents only the littoral fauna of the island; all the specimens appear to have been obtained in very shallow water on coral reefs, on mangrove roots and under stones along the shore, or in other similar localities. Moreover practically all the collecting was done in two bays or harbors of the island, the Spanish Water and Caracas Bay, which are situated close together in the southern part of the island, so that by collecting in other and more varied localities additional species could probably have been obtained, and too much significance must not be placed on the absence from the collection of a number of species widely distributed and common in other parts of the West Indian region. Yet in spite of the above limitations the collection is of more than ordinary interest and importance, for several reasons.