THE MOLLUSCS OF THE GREAT AFRICAN LAKES. 193 



short spines. The whorls are strongly sculptured, and the 

 columella is open (fig. 33). 



The mouth is ovoid^ somewhat angular, and the mantle 

 during life is prolonged into the last spine, forming a kind of 

 false siphon (fig. 30, 1). The radula is shown in the process 

 block, p. 189, and also in PI. 12, fig. 33. 



Comparative. 



In establishing by comparison the true affinities of the 

 Typhobias, I have purposely left undeveloped all those ques- 

 tions respecting the validity of the current systems of classifi- 

 cation which such a comparison will inevitably raise. This 

 course has been taken because I am now confident that the 

 Halolimnic molluscs are among the few remaining indications 

 of an ancient sea that once extended to or near the Tanganyika 

 region of the present day. The anatomical features of the 

 Halolimnic molluscs when studied together should therefore 

 throw a most important light on the inter-relationships of 

 those more modern marine genera and families which it has 

 hitherto been so hard to solve. It would be premature and 

 most unsatisfactory to view these questions from the anatomy 

 of a single Halolimnic type ; for this reason I have reserved a 

 discussion of these wider matters until I have had time to publish 

 anatomical descriptions of the remaining Halolimnic forms. 



The Typhobias have been classed by the conchologists 

 among the Melanias, being regarded by Fischer^ as a section 

 of this group equivalent to Faunus or Melanopsis. Judged 

 by their conchological characters alone it is by no means easy 

 at first sight to understand why such a classification was ever 

 made, as the Typhobia shell is almost as unlike any known 

 Mel an i a as that of a Pteroceras or a Cone. In assigning 

 a systematic position to any animal concerning which the 

 morphological study is incomplete, investigators are, however, 

 always influenced, and often rightly influenced, by whatever 

 collateral evidence respecting the habitat or modes of occur- 

 1 Pischer and Smith, loc. cit. 



VOL, 41, PART 1. — NEW SEBJES. N 



