THE TANGANYIKA PROBLEM. 
347 
This description would certainly absolutely answer for 
that of one of the new types which I found in Tanganyika, 
and to which I gave the generic name of Bathanalia 
(p. 348, lower). Although the Jurassic genus Amberleya 
shows a considerable range of specific variation, all its 
species have essentially the same characteristics as the two 
Purpurina injlata, upper, compared with Nassopsis nassa. 
varieties represented in the upper figures on the next page. 
The thin shell, the absence of all trace of epidermis, and 
the character of the whorls, as well as the sculpture and 
the character of the mouth, are all essentially the same in 
Bathanalia as they are in Amberleya ; the only point in 
which they differ is in the character of the columella, 
that of Bathanalia being generally open, while that of 
A 7 nberleya is always closed. I have, however, consulted 
Mr. Edgar Smith and others about this, and he assures 
