640 SCIENCE PROGRESS. 



throw a considerable light on the real nature of the 

 fauna to which both they and the jelly-fish belono-. The 

 Typhobias of Tanganyika which might at first sight 

 have been regarded as something of the nature of a 

 Paludina with a highly specialised shell, appear really to 

 combine the anatomical characters of Bythinia, Natica, 

 Littorina. and in some respects even of Strombus, while at 

 the same time they possess two forms of Spermatozoa, ex- 

 hibiting in this respect the characters both of a Paludina 

 and a Murex. It would appear thus that the Tanganyika 

 gastropods are not only unlike any living species, but that 

 they seem to combine the characters of several, and this is 

 exactly what we should expect to be the case if the Typho- 

 bias were a comparatively ancient form. Now what is true 

 of the Typhobias is true respecting the genera composing 

 the deep-water Tanganyika gastropods as a whole. We 

 have in these animals organisms which retain characters 

 that are found only in very distinct genera and families at 

 the present day, and the only possible inference from all 

 this seems to be that they retain the generalised character 

 of ancient forms. 



Lastly, these members of the Tanganyika Molluscan 

 group which I have examined appear, on the whole, to 

 possess characters combining those of several living marine 

 genera and not those of any ly^xc-dX fresh-iuafer forms. 



As is well known many of the fresh-water Molluscs, like 

 so many other fresh-water organisms, retain the characters 

 of certain extremely ancient forms, and it is obvious from 

 this that the forerunners of the modern fresh-water Molluscs, 

 as for example those of the Cretaceous times, would gener- 

 ally be less specialised than their modern derivatives and 

 would exhibit the remains of their ancient organisation in a 

 more marked degree. If the Tanganyika forms were the 

 persistent representatives of such types as these we should 

 expect that they would present more and better marked 

 primitive features than the fresh -water animals of the 

 present day. The fresh-water Molluscs of Tanganyika 

 however, combine a number of the generic and family 

 characters belonging to a variety of living Molluscs, and 



