THE TANGANYIKA PROBLEM. 



239 



that there is less pigmentation of the foot, which is nearly 

 white in the Tanganyika species. 



The snout is short, wrinkled, richly covered with black 

 pigment and non-protrusible. The tentacles are short, and 

 the eyes are situated on the posterior cases of these organs, 

 and not separated from them on subsidiary papillae as in 

 Nassopsis. The buccal mass is small and the radular sac 

 short, being reduced, as in the case of Typhobia and Tan- 



<€-^ 



Fig. 22. — The lingual dentition of Bythoceras iridescens. 



ganyicia, to a small swelling on the floor of the oesophageal 

 tube* 



The radular dentition is extremely interesting, a single 

 row of teeth being represented in Fig. 22. The outer and 

 inner lateral teeth distinctly resemble those of the Melano- 

 planaxoid type, which I described f in considering the 

 relationships of the genus Tanganyicia, and are something- 

 similar to those of the " Neomelanian " group of the 

 brothers Saracin ; \ while the admedian tooth is peculiar, 

 owing to the presence of two small subsidiary denticles on 



* Compare figure of Tanganyicia rufofilosa (Fig. 32). 



t Loc. cit. 



% "Die Siisswasser-Mollusken von Celebes" (Wiesbaden, C. W. KreidaPs Verlag), 



