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 
