210 FRESHWATER FAUNA 



others which cannot be so summarily dealt with : these 

 are Chytra and Limnotrochus, which find their nearest 

 affinities with marine forms, especially Capulus and 

 Aporrhais; and Spekia, which is said to be nearly allied 

 to an existing marine shell, Lamellaria perspicua. The 

 existing Lamellaria is a genus of recent date, first known 

 in the Pliocene, but it belongs to an ancient family, the 

 Velutinidse, which contains some forms not at all unlike 

 Spekia in outward appearance. Syrnolopsis, the last of 

 the peculiar Mollusca of Tanyganyika, is known only by 

 its shell, its anatomy not yet being worked out. In 



FIG. 77. Tiphobia Horei, from lake 

 Tanganyika. After Crosse, from 

 Bronn's " Thierreichs." 



addition to Mollusca with close affinities to marine 

 genera, there is also present the little jelly-fish, Lim- 

 nocnida tanganyic&a, which, however, is not restricted to 

 Tanganyika, but occurs also in the Victoria Nyanza. 

 This, w T e might suppose, must surely have been captured 

 by the isolation of a marine area : it certainly seems 

 very unlikely that creatures so sensitive to changes in the 

 composition of the environment would voluntarily make 

 their way from the sea to a river ; still, instances are 

 known in which they have gone far in this direction. 

 Dr. J. von Kennel has described lagoons bordering the 



