LAKE TANGANYIKA 



209 



of central Africa, a peculiar fauna of its own, which is 

 even more marine-looking than the Melanopsids of 

 the Pontic beds. A little jelly-fish, Limnocnida tan- 

 ganyiccBa, also occurs, the second known instance of a 

 jelly-fish inhabiting fresh water, the first (Fig. 76) having 

 been discovered in the tanks containing Victoria regia at 

 Eegent's Park; its original home is supposed to have 

 been Brazil. There are also crabs, belonging to the 

 freshwater family of Thelphusidae, some sponges, and a 

 polyzoon, Arachnoidea ray lanJcesteri. 



The molluscs are of great interest, particularly as throw- 



FIG. 76. The Freshwater Jelly-fish, Limnocodium 

 victoria. The figure on the right shows the 

 jelly-fish as seen floating. After Lankester. 



ing additional light on the anatomy of the Melaniidae 

 and Melanopsidse. According to the evidence furnished 

 by the dissection of the nervous system by Mr. J. E. 

 S. Moore, five of them are members of the Melaniidse ; 

 these are Tiphobia (Fig. 77), Bathanalia, Paramelania 

 (Fig. 78), Tanganyicia, and Bythoceras, which have a very 

 marine appearance. Another, Nassopsis, agrees in the 

 structure of its nervous system with Melanopsis, but is 

 described as possessing a labial commissure, a somewhat 

 archaic character. These, then, enlarge our knowledge of 

 an already recognised freshwater group, but there are 



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