THE TANGANYIKA PROBLEM. 265 



considered as generically distinct from Vivipara. The 

 chief of these distinctions are found in the size of the 

 animal, the remarkable characters of its shell, and in the 

 arrangement of its nerves. 



In the nerves we find a very pronounced difference from 

 Vivipara constituted by the existence of a strongly marked 

 zygoneurous connection on the animal's left side, while at 

 the same time the cerebral ganglia are closely approximated 

 together and the pleurals are applied to them below, instead 

 of being separated from the cerebrals in the manner so 

 characteristic of the Vivipara. (Compare Figs. 45 and 46.) 



Neothauma remains therefore generically distinct from 

 Vivipara, but it is doubtful whether it should be regarded 

 as a member of the Halolimnic group. 



Stanley a appears to be related to the nerilidse, and 

 therefore is probably not a member of the Halolimnic 

 group. 



