344 THE TANGANYIKA PROBLEM. 



words, they still retain the characters of a fauna belonging 

 to some departed age. This being so, it also becomes 

 apparent that it is at any rate possible that some of the 

 hard parts of these halolimnic animals, the shells of the 

 gastropods for example, the spicules of the sponges, and so 

 on and so forth, may present the structural peculiarities 

 which typify the same kind of organisms belonging to some 

 particular palseontological epoch. As a matter of fact, even 

 before I was assured of the really primitive character of the 

 halolimnic invertebrates, I had become convinced, while still 

 upon the shores of Tanganyika, that the strange shells 

 peculiar to the region were very similar to some other shells 

 either living or extinct which I had already seen elsewhere, 

 and on searching through the conchological representatives 

 of the different geological eras, it was found that the very 

 remarkable fades which the shells of the halolimnic gas- 

 tropods possess, is unmistakably again presented by a 

 similar number of gastropods, which are characteristic of 

 the deposits left by the old Jurassic seas. In following up 

 this line of investigation we have been greatly indebted to 

 Mr. Hudleston, who allowed me to examine and have 

 drawings made of the suitable specimens contained in his 

 unique collection of Jurassic forms. From this collection, 

 and from that contained in the British Museum, it was 

 possible to find types which correspond often in a specific 

 sense with the shells of the living halolimnic group. And 

 in order that the reader may fully appreciate the nature of 

 this comparison, I have reviewed in sequence the different 

 corresponding types. 



Beginning with the genus Paramelania from Tan- 

 ganyika, we find that, among the numerous fossil remains 

 of gastropods in the marine Jurassic deposits, there are a 

 number of allied forms to which the generic name of 



