ykkdenetjrg: kvolution of molluscan fauna. 261 



The connexion between the two regions was already much less direct 

 in Aquitauian times, as indicated by the much smaller proportion 

 of European species in the Gaj fauna, wliile in tlie successive faunas 

 the contrast between the eastern and western faunas approximates 

 the conditions observed at the present day. Several geolojjists, 

 amongst whom I may mention Op])enheim and Eovereto, have already 

 commented upon the similarity between the Indian Eocene and 

 Oligoceue faunas and those of Europe, as contrasted with the 

 divergence between tlie ^Miocene faunas. It is satisfactory to find 

 these conclusions confirmed by a closer studj- of the fossils tlian had 

 been practicable hitherto. It is wortb mentioning that tlie Egyptian 

 Miocene marine fauna, so far as is known, contains a large admixture 

 of Eastern forms, indicating that the land barrier between the two 

 marine provinces must liave extended across tlie Eastern Mediterranean 

 fuither north than the present isthmus of Suez. I should also 

 mention that the similarity between the Tertiary faunas is restricted 

 to those of the Lutetian and Oligocene. The Lower Eocene molluscan 

 fauna of India differs vastly from that of Europe, quite as much as 

 the faunas from the Middle Miocene. 



An attempt has been made at showing the above data in the form 

 of a diagram upon which have also been inserted the relative position 

 of the principal post-Eocene mammalian faunas of India, and also 

 some of the main geological events such as the earth-movements of 

 the Himalaya and of the Indian Peninsula, and the corresponding 

 oscillations of the sea-level, so far as can be gathered from the 

 information at present available. 



In addition to the molluscan faunas from ISTorth-Western India, 

 I have inserted the proportion of living forms in the Gastropod fauna 

 of Karikal, another Tipper Tertiary Indian fauna latterly monographed 

 by Cossmann, and. wliich, from the identity of several characteristic 

 fossils, appears to be on a level with the Hinglaj Beds, more especially 

 the Upper Hinglaj. I have thought it interesting, for the sake of 

 comparison, also to illustrate diagrammatically the much more rapid 

 evolution of the Echinoidea, and especially of the terrestrial mammalia. 



