THE TANGANYIKA PROBLEM. 241 



tomus, it is certainly in accord with the rest of the animal's 

 morphological peculiarities. 



The oesophagus and salivary glands are in all ways 

 similar to those of Ty phobia* but these characters are 

 common to so many different kinds of gastropods that they 

 are of little value from a special morphological point of 

 view. 



The stomach has two chambers, the anterior of which con- 

 tains a style. The intestine is simple, and in Tauganyicia 

 takes the course represented in Fig. 32. The rectum 

 is not dilated, nor beset with any accessory gland. The 

 bile ducts seem to open by two very small apertures upon 

 the base of the posterior stomachic chamber. Stomachic 

 valves are feebly, if at all, developed. The liver is large, 

 and occupies much the same position as Nassopsis (see 

 below). The excretory organ occupies a place in front of 

 and above the heart and opens by a minute pore at the 

 extreme upper end of the mantle cavity, Fig. 29. 



The heart has the usual ta^nioglossate characters, con- 

 sisting of an auricle, ventricle, and aortic trunk ; but the 

 last structure is much less developed in Bythoceras than in 

 many forms — as, for example, in the genus Ty phobia. 



The nervous system in Bythoceras (Fig. 23) is very 

 interesting, since it is absolutely unlike that possessed by 

 the genus Nassopsis, and closely simulates the type described 

 by Bouvierf as typical of the genus Cerithium. It also 

 strongly resembles that of the genus Tanganyicia. Viewed 

 from above, Fig. 23, the cerebral ganglia are seen to be 

 closely fused together, while the left pleural and sub-in- 

 testinal ganglion, as in Cerith'uim, form a single massive 

 trunk, which at its hinder extremity gives rise to the sub- 



* Loc. cit., " Quart. Journ. Micr. Sci.," Vol. 41, 1898, p. 190. 

 t "Ann. Dis. Sci. Nat.," 1887, PP- I 3 I * I 35» pl> vl i- 



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