1898] NOTES AND COMMENTS 299 



" The delicate nature of the lake medusae, and the fact that 

 most of the Halolimnic molluscs are exclusively deep-water forms, 

 renders it impossible that these organisms can have made their way 

 into Tanganyika at any time under the physical conditions which 



now exist. 



" The facts of distrilmtion and the general character of these 



. forms, as well as the geographical conditions of the lake in whicli 



they are now found, lead then to the conclusion that the Tanganyika 



region of Central Africa must have approximated to a deep arm of 



the sea in ancient times. 



" This view is finally confirmed by the details of the anatomy of 

 the Halolimnic animals themselves. For some of the individual 

 molluscs of this group combine the characters of several of the 

 most modern marine genera. The Halolimnic fauna of Tanganyika, 

 therefore, cannot represent an extinct fresh-water stock, since the 

 characteristic fresh-water organisms of tlie present day (which 

 would, in such a case, have to be regarded as their linear descen- 

 dants) possess the anatomy of vastly older types. 



" To the Halolimnic animals there thus attaches the unique 

 interest that they themselves constitute the few surviving indica- 

 tions of an old sea which once extended far into the African 

 interior, and which, judging from the characters of the animals it 

 left behind, must have retained its connection with the ocean at 

 least as late as Tertiary times. 



" These conclusions, it will be observed, are directly in opposition 

 to the viev^s which were originated by Murchisou, and which depict 

 the African interior as never having been below the sea, at least 

 since the New Red Sandstone age." 



Some New Bivalves 



Theee is evidently much work to be done amongst small bivalves. 

 Most collectors shirk them owing probably to the difficulty they find 

 in discriminating between young individuals of large species and 

 genuine small forms. Mr Felix Bernard's researches into the 

 development of the hinge in the Pelecypoda are, however, doing 

 much to make the task easier ; whilst to the fact that in the course 

 of his studies, small shells have of late principally occupied his 

 attention, must be due his numerous recent discoveries of minute 

 but fully grown pelecypods. Three new genera are now founded 

 by him {Bull. Mils. Hist. Nat. Paris, 1897, pp. 309-14) on 

 specimens in material from Stewart Island, near New Zealand. One 

 of these, Pachykellya, belongs to the family Erycinidae, the other 

 two, Cyamiomactra and Ferrierina are doubtfully referred to the 

 Mactridae. The first named measures but 1 x 2 mm. and the second 

 4-5 X 3 mm. The third is, however, perhaps the most interesting. 



