THE MOLLUSCS OF THE GREAT AFRICAN LAKES. 189 



" bile-ducts " (fig. M, 2, 3) . The anterior chamber is separated 

 from the posterior chamber of the stomach by a constricted annu- 

 luS; and the anterior chamber encloses and is almost filled by a 



Central and three lateral teeth of the radula of Typhobia (upper figure) and of 

 Bathanalia (lower figure). Three lateral teeth on each side and a central 

 tooth constitute the unit, which is repeated row after row along the radula. 



large crystalline style, represented in fig. 44, 5). The whole 

 arrangement of the stomach, the position of the folds and aper- 

 tures, the separation into a posterior and an anterior chamber 

 or csecum, and the presence in the latter of a crystalline style 

 are all similar to the condition of things obtaining in Pterocera. 

 The style and its sac are undoubtedly homologous with the 



