THTi] MOLLUSCS OF THE GREAT AFEFCAN LAKRS. 187 



The Molluscs of the Great African Lakes. 

 IV. Nassopsis and Bythoceras. 



By 

 J. E. S. ITIoore. 



Willi Plates 20 and 21. 



Among the numerous forms of molluscs that appear to he 

 peculiar to Lake Tanganyika at the present time, there are 

 three very marked genera — Paramelania, Nassopsis, and 

 Bythoceras, which, owing to the suhstantial similarity exist- 

 ing hetween their shells, might, and have hitherto been 

 regarded as closely associated forms. The first of these to be 

 discovered, Nassopsis, was originally classed by S. P. Wood- 

 ward ^ among the Melanias, and as a member of the sub-genus 

 Melanella, his determination being made from some empty 

 shells which had been brought from Tanganyika by Captain 

 Speke, during Burton^s celebrated journey to that lake. The 

 second genus, Paramelania, was formed by Smith,^ in 1881^ 

 to include a somewhat similar form of empty shell which had 

 been brought from the same locality by the missionaries; and 

 to distinguish the members of this genus from the original 

 Melanella nassa of Woodward, Smith^ placed the latter form 

 in the new genus of Nassopsis. 



In 1896 I* dredged in the deep water of Tanganyika 



' « Zool. Soc. Proc./ 1857. 

 ' Ibid., 1881, p. 559. 



3 'Ann. Mag. Nat. Hist.,' 1890, vol. vi, p. 93. 



•* The genus was first named in my paper in the ' Proc. Roy. Soc.,' vol. 

 Ixii, p. 451. The full diagnosis is contained in the ' Proc. Mall. Soc.,' 1898. 



