194 J. E. S. MOORE. 



rence of such a form may be to hand. It was thus well 

 known when the strange Typhobia shells were first described, 

 that they came from a great equatorial fresh-water lake, and it 

 appears to me that the early investigators only did the best 

 they could with the purely conchological material they had 

 before them, in concluding that although the shell of Ty- 

 phobia had few characters in common with those of the 

 Melaniidse, they probably belonged to this group all the same. 

 The Typhobias, however, happen to be one of those rare 

 organisms in dealing with which, unless there is ample mor- 

 phological material to draw upon, common sense anticipations 

 such as the above are almost certain to be wrong. There 

 was no reason when the Typhobias were originally described 

 to suppose that Tanganyika, the great fresh-water lake in the 

 centre of the African continent, had ever been connected with 

 the sea. It was not known then that jelly-fish inhabited the 

 lake, or that the Typhobias were only one in a long series of 

 Gastropods which are not known to be living anywhere else 

 in the world. Progressive zoological exploration has com- 

 pletely changed our views. The study of the distribution of 

 the molluscs in the great African lakes points strongly, as I 

 have shown, in the direction of the marine origin of the Halo- 

 limnic group of animals. We might, therefore, now with 

 reason tend to be prejudiced in the opposite direction, i.e. in 

 favour of the marine affinities of all the Halolimnic forms. 

 Such a conception will, however, as I pointed out in my paper 

 on the distribution of these forms,^ require the very strongest 

 morphological support, since it comes into the most uncom- 

 promising conflict with all those geological speculations re- 

 specting the character of the interior of Africa which were 

 started by Murchison, and which affirm that the African in- 

 terior has never been beneath the sea, at least since the period 

 of the New Red Sandstone.^ It is necessary, therefore, to use 

 the greatest caution in determining what the affinities of the 



1 This Journal, p. 159. 



2 See also Gregory's re-statement of this view contained on p, 214 of his 

 work 'The Great Rift Valley,' published in 1896. 



