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Show 1906.] CRUSTACEA OF THE THIRD TANGANYIKA EXPEDITION. 203 merus; dactylus, including terminal spine, about one-fifth of propodus, with two spines on lower edge. Fifth peraeopods (Plate X I V . fig. 71) with propodus longer than merus ; dactylus, including terminal spine, one-fifth of propodus, with about 26 spines on lower edge. Total length, female (not ovigerous) 15 m m. Remarks.-This species is very similar to the preceding, but appears to be sufficiently distinguished by the longer rostrum, the longer spines on first segment of antennular peduncle, and the smaller number of spines on dactylus of last peraeopods. Occurrence.-Mbete, 1.x.04. " Taken on rocks, shallow water." Two specimens. Kala, 19.xi.04. "Taken on rocks, shallow water." Two specimens. iii. General Remarks. So far as the Macrurous Crustacea are concerned, the chief result of Dr. Cunnington's Expedition has been to render still more striking the great richness and peculiar character of the fauna of Tanganyika as compared with that of the other lakes of Central Africa. While Nyasa and Victoria Nyanza have yielded only a single species which, with its varieties, has an enormously wide geographical range from the Nile (and perhaps Algiers) to Natal on the south, and to Queensland and New Caledonia on the east, every one of the twelve species found in Tanganyika is, so far as we yet know, peculiar to that lake. Of these, Pcdcemon moorei belongs to a genus having a very wide distribution in the fresh-waters of tropical regions; but while a number of species are known from East and West Africa, P. moorei is the only one yet found in the region of the great lakes. Apart from its very small size, the species does not present any very unusual or striking characters, and it is therefore impossible to attach any great importance, from the point of view of zoogeography, to its supposed affinities with other species. It may be noted, however, that all the species with which it is found possible to compare it closely are inhabitants of the East African and Oriental regions, and that the species from the Nile, while undoubtedly distinct, does not differ in such a way as to exclude the possibility of phylogenetic connection. With the remaining eleven species, belonging to the Atyidae, the case is very different. They represent three genera which, so far as is yet known, are peculiar to Tanganyika, and which differ from all the other genera of the family in having a smaller number of branchiae. Whether this single common character indicates a phyletic connection between the three genera is doubtful. The resemblances between Limnocaridina and Caridina, and between Atyella and Atya or Ortmannia, would suggest that the reduction of the gills had taken place independently in the two cases. At the same time, Bouvier's very interesting discovery (C. R. Acad. Sci. cxxxviii. p. 446, 1904, and Bull. Sci. France et Belgique, xxxix. |