1906.] CRUSTACEA OF THE THIRD TANGANYIKA EXPEDITION. 203 



mervis ; dactylus, including terminal spine, about one-fifth of 

 propodus, with two spines on lower edge. Fifth peraeopods 

 (Plate XI Y. 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 mm. 



Remarhs. — This species is very similai- to the preceding, but 

 appears to be sufiiciently distinguished by the longer rostrum, the 

 longer spines on first segment of antennular peduncle, and the 

 smaller number of spines on dactylus of last perteopods. 



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 Hemarks. 



So far as the Macrurous Crustacea are concerned, the chief 

 result of Dr. Ounnington's Expedition has been to i-ender still 

 more striking the grea,t 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 ISTew 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, Palcemon 

 moorei belongs to a genus having a very wide distribution in the 

 fresh-waters of tropical regions ; but while a number of species 

 are kno\\Ti 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 sti'iking 

 chara^cters, and it is therefore impossi]:)le to attach any great 

 importance, from the point of view of zoogeography, to its 

 supposed aflinities 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 Afi-ican and Oriental regions, 

 and that the species from the Nile, while undoubtedly distinct, 

 does not difier in such a way as to exclude the possibility of 

 phylogenetic connection. 



With the remaining eleven species, belonging to the Atyidfe, 

 the case is very different. They represent three genera which, so 

 far as is yet known, are peculiar to Tanganyika, and which difier 

 from all the other genera of the family in having a smaller number 

 of branchiae. W^hether this single common character indicates a 

 phyletic connection between the three genera is doubtful. The 

 resemblances between Lininocaridina 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. 



