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 ; j while the admedian tooth is peculiar, 
owing to the presence of two small subsidiary denticles on 
* Compare figure of Tanganyicia rnfofilosa (Fig. 32). 
t Loc. cit. 
\ “ Die Siisswasser-Mollusken von Celebes ” (Wiesbaden, C. W. Kreidal’s Verlag), 
1898. 
