It was in the spring of 1920 that, especially through the kind co-operation of Prof. SLUITER, I was enabled to carry out a long cherished plan of studying and collecting the rich Fauna of tropical seas. As a conservator at the Zoological Museum of Amsterdam I had handled so much material, collected by the Siboga-Expedition in the East-Indies and, while working over the Madreporaria of this Expedition, I examined so many dead corals, that an increasing desire arose in me to study and collect the rich Fauna of tropical seas and to see live corals myself. After some reflection it became clear that the island of Curaçao was the locality best fitted for my purpose. I had only a short time at my disposal and, as I intended visiting the United States too, I was assigned to the West-Indies. Of all West-Indian islands Curaçao is within easiest reach of Holland, but there were other and weightier reasons why I picked out this island. The West-Indies have been rather well explored by different Expeditions, with the exception of the Southern and South-Western part of the Caribbean Sea. In 1884 the „Albatros” visited Willemstad for a week and Dr. JAMES E. BENEDICT and Mr. W. NYE, the naturalists of that Expedition, made extensive collections, while in 1895 Dr. J. VERSLUYS, on board of the yacht „Chazalie”, collected at different localities in the Southern part of the Caribbean and spent a.o. one day in the Schottegat near Willemstad. However the short time spent by these two Expeditions in this part of the Caribbean made a more than casual survey of the very rich Fauna impossible. In 1904 and 1905 Dr. J. BOEKE ¹) made for the Dutch Government a trip to Curaçao and the other Dutch West-Indian islands to study the fisheries there and he made an extensive collection of fishes, studied and described by Dr. J. METZELAAR ²), as also of crustaceans which have been worked over by Miss RATHBUN ³). It is logical that, owing to the nature of his commission, this collection of Dr. BOEKE bore an onesided character. Thus it remained a desideratum to look for and collect other forms of the Fauna of those waters.