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 are 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 
