436 MR. J. E. S. ilOOEE OS THE RESULTS [May 4, 



necessary, for the moment the peculiar character of its caudal 

 bristles was shown not to be sexual, it was evident that it could 

 no longer be confounded with the more normal-tailed species. 

 Adult examples of both sexes were present in the series, as was 

 also the case with the Xyasan P. tetradavtyJus. 



. Mr. Howard Saunders, F.Z.S., exhibited on behalf of Mr. Henry- 

 Evans a series of instantaneous photographs, taken in the Outer 

 Hebrides, of the Great Grey Seal {Haliclioerus gnjphus) in various 

 attitudes. 



The follo\\ing papers were read : — 



1. On the general Zoological Results of the Tanganyika 

 Expedition. By J. E. S. Moore. 



[Eeceived April 4, 1897.] 



The object of this expedition to Tanganyika was to collect materials 

 sufficient for the more complete determination of certain special 

 forms of animals. At the time I started our knowledge of the famia 

 of the great lakes was in a most imperfect condition. It had been 

 ascertained by Boehm in 1883 that a Medusa inhabited Tanganyika ; 

 and through the examination of the empty shells of the various 

 molluscs brought back by travellers from the Interior it had been 

 determined that the great lakes contained examples not only of 

 species and genera which are normal to fresh water, but of others 

 which but for their known lacustrine habitat would certainly have 

 been regarded as marine. It was impossible, however, with the 

 material then at our disposal, to say whether the deviations from 

 the usual characters of the fi-eshwater faunas found in Central 

 Africa were likely to be due to convergence of evolution, i. e. 

 parallel development, or to the lakes having been actually con- 

 taminated by oceanic forms. Neither could it be determined, 

 supposing the lakes to have been thus contaminated, whether the 

 marine forms they exhibited were like anything at pi-esent existing 

 in the sea, or whether they had persisted or become modified from 

 a more ancient marine stock \Ahich has elsewhere disappeared. 

 The probability of these forms having resulted from marine con- 

 tamination is ob^iously greatly affected by the question whether 

 they are locally or m idely distributed as African freshwater forms. 

 If they are widely distributed, it is quite likely that Africa possesses 

 animals which are not at present known to inhabit lakes elsewhere. 

 If, on the other hand, they are extremely limited in distribution, 

 it is probable that the existence of these enigmatical animals has 

 resulted through the coutamiuation of the great lakes, either in 

 the past or the present, by animals from the sea. 



In the first place, it will be necessary to see if a widespread 

 similarity in the African lake-faunas is in the nature of things 

 possible, and, in order to ascertain this, it is essential to examine 



