348 



THE TANGANYIKA PROBLEM. 



me that such differences cannot be upheld as generically 

 distinctive, more especially as the amount of umbilical 

 opening in Bathanalia varies a good deal in extent from 

 shell to shell. We may, therefore, conclude that, concho- 

 logically, Bathanalia and Amber ley a are the same. 



Two varieties of Amberleya, upper, compared with Bathanalia howesi, lower. 



Among the Jurassic fossil gastropods there aie a number 

 of forms which are typified by the so-called Littorina sulcata, 

 and if the figures of the two specimens of this form given 

 on p. 349, lower, be compared with the back and front view 

 of the shell of Limnotrochus thomsoni from Tanganyika 

 given on the same page, it will be realised how closely the 



