162 J. E. S. MOORE. 



importations from the sea. Now such a fauna is presented to us 

 in that of Tanganyika at the present day, for in this lake there 

 have been known to exist ever since 1859 what appear to be 

 the shells of some six genera of Gastropods^ which are entirely 

 unlike any known fresh-water forms, while their shells at 

 the same time simulate several modern oceanic types. The 

 interest in these strange molluscs, which have been known 

 hitherto only by their conchological characters, was greatly 

 augmented when in 1883 Boehm found jelly-fish in the lake; 

 and during my recent expedition I have been able to add 

 deep-water crabs, prawns, sponges,^ and Protozoa to 

 this anomalous list of organisms, all of which appear to 

 possess the same marine afl&nities. 



It is ray object in the present paper, to ascertain to 

 what conclusions as to the nature and origin of this anoma- 

 lous series the facts of distribution lead ; while in those which 

 follow I shall deal with the morphological affinities of the 

 hitherto unknown individual forms, and thus determine whether 

 the conclusions to which these facts of distribution seem to point 

 are really sound. Almost no definite observations have been 

 hitherto available for the study of this subject, and consequently 

 the material contained in this and the following papers will be 

 mostly new. I would, therefore, invite particular attention to 

 the positive character of the evidence which 1 shall bring 

 forward in support of the recent marine origin of a number of 

 the animals contained in Tanganyika, as compared with the 

 wholly negative character of that upon which the geological 

 speculations of Murchison respecting the '' permanence of 

 terrestrial conditions ^' in the African interior at present rest. 



To believe that the marine animals of Tanganyika are among 

 the few remaining indications of a sea that once extended to 

 the very heart of the African continent is to come into the 

 most uncompromising conflict with the theory put forward by 



' The affinities of the deep-water sponge which I obtained in Tanganyika 

 have not yet been determined, but its striking external character and its 

 remarkable deep-water habitat have inclined me to regard it as a member of 

 the anomalous section of the fauna which the lake presents. 



