THE TANGANYIKA PROBLEM. 



2 5* 



obtained by Smith, Guatkin referred it to the types 

 approximating to the genus Cerithium, while Smith 

 himself remarked upon its similarity to the radula of the 

 Planaxidae. It also corresponds very closely to the radulae 



Fig- 34- — Semi diagram of the anatomy of Nassopsis nassa. The 

 mantle has been cut open from above, and the nervous system is 

 seen from above in black. Opposite sin., the gill ; cryst. s., 

 crystalline style ; sp. r., spiral caecum ; si., stomach. 



of several Littorinas. The oesophagus is long, narrow, 

 and simple, and leads into a large stomachic chamber, on 

 the walls of which there are numerous glandular folds, 

 and a very curious and striking spiral caecum on the 



