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 Ambevleya 

 shows a considerable range of specific variation, all its 

 species have essentially the same characteristics as the two 



Purpurina /////a/a, 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 Ambevleya ; the only point in 

 which they differ is in the character of the columella, 

 that of Bathanalia being generally open, while that of 

 Ambevleya is always closed. I have, however, consulted 

 Mr. Edgar Smith and others about this, and he assures 



