1899.] CRrSTACEASS PROM LAKE TANGANYIKA. 711 



pi. vii. f. 2) and Klunzinger (Zeitschr. f. wiss. Zool. xvi. 1866, 

 p. 357, pi. XX.), appears to present distinctive characters. Both 

 these authors figure the rostrum with a very convex upper 

 edge. Kkmzinger gives the number of serrations as "^ , Roux 

 figures '^. According to the figures of both authors, however, not 

 more thau one tooth appears to be behind the orbit. Both show 

 the carpus of the 2nd ])er.'eopod to be distinctly shorter thau the 

 merus, and much more than half the length of the hand. Kiunz- 

 inger's figure of the chela shows it to be more slender, with the 

 palni less inflated and the fingers longer than in our species. 



Neither of the species described in this paper can be depended 

 on as throwing any light on the general question of the origin of 

 the Tanganyika fauna. The genus Palcemon contains about 50 

 species, of which only two are said to be marine. It is closely 

 allied to Leander, in which, conversely, the marine species greatly 

 predominate, while both genera have numerous allies among the 

 littoral fauna. Whatever bearing the genus Palcemon may have 

 on the more general problem of the origin of freshwater faunas, 

 the number of its species, their wide distribution, and . lastly the 

 imperfect nature of the specimens from which the present species 

 is described (precluding any conclusion as to its nearest speciSc 

 affinities) all I'ender it incapable of serving us towards the settle- 

 ment of the special problem of Tanganyika. 



Limnocarklina belongs to the Atyidce, a circumtropical 

 family of freshwater forms whose probably somewhat distant 

 allies are supposed by Ortmann to be found in the deep-sea 

 Acanthepliyridce. It is a near ally of Caridina, an extensive 

 genus, of which one species is known from the West Indies, while 

 the rest occupy countries bordering on the Indian Ocean from 

 S. Africa to Australia ; one species occurs in the Nile and the 

 rivers of Algeria. One species, C. wydii, has a range extending 

 from East Africa to Queensland and Celebes. It is notew-orthy 

 from the point of view of the present case that Caridina is not 

 known to occur in West Africa. Our form from Tanganyika is 

 in the meantime an isolated species, and the characters that it 

 presents are not those of a primitive type, but rather of a somewhat 

 specialized form. 



EXPLANATION OF THE PLATES. 

 Plate XXXIX. 



Fig. 1. Limnocariclina favganyikce, g. et. sp. n., §, p. 704. 



2. „ ,, Carapace and rostrum. 



3. Caridina wi/c^ii (Hickson), p. Tf^o. Anterior part of carapace. 



4. Limnocaridina tanganyihm, p. 704. Peduncle of antennule. 



5. „ ,, Mandibles. 



6. „ ,, First maxilla. 



7. ,, ,, Second maxilla. 



8. „ ,, First maxilliped. 



9. „ Third maxilliped. 9 a. Terminal joint of 



third maxilliped. 



46* 



