294 
THE TANGANYIKA PROBLEM. 
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. 
Limnocaridina belongs to the A l y idee, a circumtropical family of freshwater 
forms whose probably somewhat distant allies are supposed by Ortmann to be found 
in the deep-sea Acanthephyridre. 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. wyckii , has a range 
extending from East Africa to Queensland and Celebes. It is noteworthy 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. 
