THE TANGANYIKA PROBLEM. 



2 35 



The lingual dentition (Fig. 18) presents some of the 

 features of that of Chytra, but it differs considerably from 

 that form, more so in fact than is usually the case in closely 

 allied mollusca. 



In the general structure of the mantle complex, Limno- 

 trochus is similar to Chytra. 



The nervous system of this genus differs considerably 

 from that of Chytra. In the first place, the cerebral 

 ganglia are separated by a distinct commissure. The supra- 



Fig. 19. — The nervous system of Limnotrochus thomsoni dissected from above. The 

 pedal ganglia not shown. (From a drawing by Miss Digby. ) 



intestinal cord is fairly long, and there appears to be a 

 distinct dyaloneurous relationship of the pallial nerves on 

 the left. The sub-intestinal cord is shorter than in Chytra, 

 and the sub-intestinal ganglion is directly connected with 

 the right pleural ganglion by a rather stout and short 

 commissure ; the animal being, consequently, according to 

 Bouvier's definition, strictly zygoneurous on the right. 

 Another striking peculiarity of the nervous system of 

 Limnotrochus is apparent on making a lateral inspection of 



