272 THE TANGANYIKA PROBLEM. 



as Pleurotornaria and Trochus* From the character of 

 the nervous system and the radula of CJiytra we should 

 have no difficulty in deciding at once that it comes very 

 near the genus Capulus and its modern allies. But since it 

 is not superficially modified either in its shell or foot, and 

 retains the two very primitive characters in its alimentary 

 apparatus which have just been described, and which neither 

 the living Capulidae nor their allies are known to possess, it 

 is obvious that CJiytra is ancestral with respect to them. 

 But further, CJiytra is possessed of many points of resem- 

 blance to XenopJiora, and this resemblance is by no means 

 confined to the shell. The nervous system of CJiytra may 

 be said to stand half-way between that of Capulus on the 

 one hand and XenopJiora on the other. In the same way 

 CJiytra shows in the character of its foot an incipient stage 

 in the modification which reaches its maximum in Strombus 

 and Aporrhais and their modern allies. These considera- 

 tions indicate that we have in CJiytra a form which quite 

 satisfactorily connects up two fairly ancient marine groups, 

 for it possesses the characters of Capulus and its allies, and 

 also those of the Xenophoridse themselves. 



In LimnotrocJius we have, as I have pointed out, an ally 

 of CJiytra, and the same inferences may be drawn from its 

 structure. 



Turning now to the group of gastropods composed by 

 the genera Paramelania and BytJioceras and their subordi- 

 nate species, we find that all these forms, both in their 

 radulae and nerves, present us with features which are dis- 

 tinctly similar to those of CeritJiium ; but they are at once 

 dissociated from the Cerithoid group of Prosobranchs, by 

 the peculiarities of their gastric apparatus and their posses- 



* It has since been found in a reduced condition in Turritella communis. See paper 

 by W. B. Randies, " Anat. Anz." 1902 ; Bd. xxi., p. 201. 



