810 J. E. S. MOOKE. 



going to compare the halolimuic fauna, at least a sufficient 

 number of types which are similar to individual halolimnic 

 forms to correspond with a majority of the forms the halo- 

 limnic fauna now contains. I have emphasised this point 

 because certain comparisons have already been instituted 

 between the shells of the Pararaelauias of Tanganyika and 

 forms occurring in the fresh-water cretaceous beds. 



In 1883, White/ in an extremely short paragraph, pointed out 

 that, speaking conchologically, there is not much to distinguish 

 the shell of the genus Paramelania (Smith) from that be- 

 longing to the extinct fresh-water Pyrgulifera, which he 

 obtained from the Green River deposits of the United States. 

 So far as the outward forms of these shells go, there are slight 

 differences as to sculpture, and so forth (compare PI. 23, figs. 

 1 and 7). But I do not know that such dissimilarities as 

 these would justify even a conchologist in regarding the genera 

 as distinct, and that this comparison of a single halolimnic 

 and cretaceous shell is, in the absence of any possibility of 

 information respecting the nature of the contained animals or 

 their associates, " so fai', so good," seems to be the total net 

 result of the further observations made upon the subject by 

 Tausch^ and Oppenheim,^ except that these latter authors 

 appear to have had at their command more extensive and 

 better preserved material than that which White examined. 

 Speaking conchologically, then, there is one type in the creta- 

 ceous fresh-water deposits and one in the African halolimnic 

 fauna which are similar in form. But even in the case of the 

 single correspondence which presents itself Tausch's work 

 appears to have rendered it extremely doubtful whether the 

 two forms can be still considered as even conchologically the 

 same. He showed, after examining hundreds of Pyrguliferas 

 from the upper cretaceous beds from Ajka in Hungary, that 



1 'Proc. U.S.A. Nat. Mus.,' S. 98, Washington, 1882, p. 98 (published in 

 1883). 



* 'Sitz. Ber. d. k. Acad. Math. Wien,' 1885, Bd. xc, p. 57. 



3 Zeitschrift. der Deutscli. Geol. Gesell.,' 1892, Bd. xliv, p. 697; for 

 diagnosis of Pyrgulifera see ' U.S. Geol. Surv.,' 40 parallel, vol. iv, p. 146, 

 pi. 7, fig. 19. 



