OP THE HALOLIMNIC FAUNA OF LAKE TANGANYIKA. 347 



importance in considering the origin of the halolimnic fauna, 

 being outside any possible connection with the Congo basin. 



African Jurassics (^Madagascar and Ahyssinia). — Briefly 

 referring to a valuable paper by Messrs. Baron and Newton on 

 fossils from Madagascar,* we may note that the Jurassic fossils 

 of that region are fairly numerous, the followmg horizons 

 having been determined by means of the ammonites : viz., 

 Oxfordian, Callovian, Bathonian, Bajocian and Lias. Amongst 

 the Gasteropoda were two species of Ccrithium from the 

 Oxfordian. The remainder of the gasteropods were mostly 

 from the equivalents of the Great Oolite (Bathonian), and 

 inchided Nerita Bwvignieri, M. and L. together with species of 

 Ncrinoia and Natica described by Morris and Lycett ; also 

 Solarium and Trochus, and likewise a new species of Opistho- 

 branch of large size referred by Mr. jSTewton to Trochactceonina. 

 Along witli this limited assemblage of gasteropods occur a very 

 considerable number of lamellibranchs. A peep at Jurassic 

 times almost under the equator is interesting in this connection, 

 but there is nothing in the Madagascar fauna which particularly 

 reminds us of the halolimnic gasteropods of Tanganyika. 



The very important development of Jurassic limestones in 

 Abyssinia described by Dr. Blanford, is extremely interesting 

 from the fact that undoubted marine beds of Jurassic age 

 have been raised, in a district situated about 10° IST. of the 

 .equator, to plateau elevations of 8,000 feet. Nevertheless, owing 

 to their apparent poverty in gasteropods, these beds throw no 

 light upon the question with which we are at present 

 .concerned.! 



Character of Fresh-water Faunas. — The second independent 

 •consideration of which I propose to treat relates to the character 

 of fresh-water faunas, and more especially of the moUusca, and 

 this, though a large subject, must be treated briefly. Without 

 going back into the very remote past, we possess a considerable 

 number of fresh-water forms, interlarded as it were with those 

 of marine origin, in the Coal-measures. This subject has 

 received much attention from Dr. Wheelton Hind, and it is 

 interesting to note that most of these forms are lamellibranchs, 

 hence they are, to a certain extent, outside the subject more 

 -especially under consideration. Gasteropoda in the really 

 fresh-water beds of the Coal-measures are rare. 



The earliest appearance of Pcdudina ( Vivipara) in this 



* Quarterly Journal, Geological Society, vol. 51, pp. 57-92. 

 t Blanford, Geology and Zoology of Abyssinia, 1870. 



