Vol. 54.] 



AND THE CORALLINE CKAG. 



311 



The names of the 15 species found at Lenham, but not in the 

 Coralline Crag, are as follows : — 



Extinct Forms. 



Miocene. 



Italian 

 Pliocene. 



Red Crag. 



TercbTd (zcumincttci Bors 



* 



* 



possibly 

 derivative. 



* 



Triton heptaoonuTfi, B roc 



PleuvotoMd consobTtncb, ^G^ 



„ Jou(i)ietti,li)Qsui 



tuTrifera^ Nyst ^ 



Xcnophova sp 



Pecten sp. nov 



„ sp. nov 



CoLfdiion, sp. nov 



Tellina Benedenii, Nyst ^ 





Southern Forms. 









Area diluvii, Ijain 









CdTdiuni 'pcipillosum, Poll 



Gastrana fraailis. Linn 



*' U ' 



Northern and Southern. 









Nuculci sidcata, Bronn 



* 



* 



* 



Trochus cinerarius, Linn. (North African) 



Besides employing the time-honoured method of testing the 

 .comparative age of any Tertiary horizon, namely, by observing the 

 proportion between its recent and extinct shells, we may go a step 

 farther back, and enquire what percentage were survivors from 

 earlier, that is from Miocene seas, or may have existed at the same 

 period elsewhere, under different conditions, in deposits which, 

 though contemporaneous, are not homotaxial. 



The resemblance of the molluscan fauna of the Coralline Crag to that 

 of the Mediterranean at the present day has often been emphasized, 

 but a similar correspondence exists, and for the same reason, between 

 the molluscan fauna of the Miocene deposits of Northern Europe 

 .and that of the Pliocene of Italy and Sicily. Many species which 

 flourished in the North Sea during the Coralline Crag period have 

 now become extinct there, but they continue to exist in the Medi- 

 terranean ; so, dealing with an earlier period, we find that a large 

 number of moUusca occurring in the Belgian^ and North German 

 Miocene/ which had disappeared from these latitudes before the 



^ Found also in the Diestien Beds of Belgium. 



^ Van den Broeck, ' Esquisse G^ol. & Paleont. des Depots Plioc. d'Anvers,' 

 1876, p. 40, etc. 



^ Von Koenen, ' Mioc. Nord-Deutschl. u. seine Molluskenfauna/ Cassel, 

 1872 ; Stuttgart, 1882. 



