2 4 o THE TANGANYIKA PROBLEM. 



the inner face (Fig. 22), a very peculiar feature, and one 

 which is only exemplified in the radula of Tympanotomies. 

 The presence of this peculiarity, together with the general 



Fig. 23. — The nervous system of Bythoceras irides- 

 cent, as seen from above, e.g. , Cerebral ganglion. 

 sub. int. g., Subintestinal ganglion. 



character of the radula, should certainly be regarded as of 

 weight in diagnosing the nearer affinities of this form. 

 And, as we shall see in placing it along with Tympano- 



