The Phylactolaemata-fauna of Curaçao, Aruba and Bonaire, as it appears from the samples collected by dr P. Wagenaar Hummelinck, is connected with the fauna of the South-American mainland. The material belongs to three species only: Hyalinella agilis — Curaçao, Aruba, Bonaire — in temporary or semi-permanent pools, rarely in (possibly) permanent pools (e.g. Sta. 44), and in rock crevices (Sta. 58) — in water with about 30-2000 mg Cl/1. Hyalinella osburni — Aruba, Bonaire — in temporary muddy pools — in water with about 40-200 mg Cl/1. Plumatella annulata — Curaçao, Klein Bonaire — in a temporary muddy pool (Sta. 82) and in cavern water of a limestone plateau (Sta. 61) — in water of about 400-500 mg Cl/1.