Much has been said of the geographical relations and the origin of the West Indian fauna, especially as to that of its vertebrates and mollusks. Mostly the islands off the Venezuelan coast, for the greater part within sight of the South American continent, remained out of question, although obvious differences between the fauna of Curaçao and that of the adjacent mainland were rather quickly noticed and its affinity towards the fauna of the Greater Antilles even emphasized (Bland, 1861; Baker, 1924). Without going into the West Indian fauna as a whole, or the current theories that try to explain its distribution, an attempt is being made to find out what palaeogeographical indication is given by the fauna of the Leeward Group, by careful examination of the distribution of its mammals, reptiles, amphibians, fishes and mollusks, — these being the only groups, perhaps with exception of the birds, which are sufficiently well known to serve as a base for zoogeographical considerations. Biocoenoses were not studied, only the distribution of species and subspecies was taken into account. The biotopes usually being very small and scattered by many isolating factors formed by accidental circumstances, the fauna being very poor and the biology of the species practically unknown, it will be clear that we have to be unpretentious in our aim and very careful in our conclusions.