No. 6. — Zoological Results of a Fifth Expedition to East Africa VI Decapod Crustacea 1 By Fenner A. Chace, Jr. U. S. National Museum As might be expected of the first extensive collection of fresh-water crabs to be recorded from the highlands of Nyasaland, at least two of the five species collected by Mr. A. Loveridge apparently were previ-ously undescribed. One of the remaining three forms is the rather striking Potamon (Potamonautes) orbitospinus Cunnington from Lake Nyasa. Another is a species which is tentatively identified as P. (P.) hilgendorfi (Pfeffer), previously recorded from various localities in Kenya Colony, Uganda, and Tanganyika Territory. The last species, which may be a third undescribed form, is represented by a single immature female. A list of the African fresh-water crabs is given in Chace, 1942. Several authors have expressed regret at the tendency to propose new names for African potamonids on insufficient evidence and have suggested that the total number of species is likely to be considerably reduced when the variations of the valid forms can be correctly evalu-ated. There is certainly little excuse for describing as new a single immature or incomplete specimen, but to assign a specific name to material from an area far removed from the known range of that particular species, merely because the apparent differences are slight and may eventually be accounted for by normal variation, seems equally blameworthy. It is probable that the potamonid fauna of Africa, like other similar faunas, is made up of a few variable species with extensive ranges and a larger number of more or less isolated forms distinguishable by constant though relatively minor characters. The true picture will become clear only when good series of specimens of different ages, like those collected by Air. Loveridge, become available from many localities throughout the African continent. It is usually a simple matter to synonymize names accompanied by adequate descriptions, once the limits of variation are determined, whereas it may be far more difficult to decide whether or not a lot of specimens assigned to a previously described species, with few or no comments, was correctly identified. 'Published with permission of the Secretary of the Smithsonian Institution.