THE TANGANYIKA PROBLEM. 



219 



Nassopsis nassa, and Lithoglyphus zonatus, the first 

 being supposed at the time to represent an aberrant form 

 of the great tropical and sub-tropical family the Me- 

 laniadce. Although nothing whatever but the shell was 

 in his hands at the time, Woodward went further than 

 this in the determination of the relationships of these 

 molluscs, relegating Nassopsis to the sub-genus of the 

 Melaniadce, Melanella. Subsequently, in 1880, a much 

 more extensive collection of shells was brought to England 

 by the captain of the small steamer which the London 



Fig. 1. — Back and front view of the shell of Melanin admirabilis — Cerethium 



subscalari forme. 



Missionary Society had put on the lake, and the still empty 

 shells which were thus obtained were figured and described 

 by Mr. Edgar Smith in 188 1. Smith, like Woodward, 

 drew attention to the extraordinarily marine aspect of 

 these forms, specially pointing out the unique trochiform 

 character of the shell of Limnotrockus, and the almost 

 exact conchological identity which subsists between the 

 shells of the Tanganyika Syrnolopsis and the marine 

 genus Syrnola. Speaking of the curious marine appear- 

 ance of these shells, Smith also drew attention to the 



