MOLLUSCA OF INDIA. 



229 



them from genera of the same family occupying other parts of India. 

 Without enumerating the many genera and species of other families 

 which are quite peculiar and restricted to this Peninsula, the 

 number of genera I have brought to your notice in this Address 

 is large and characteristic of isolation. Nor is this more than 

 might be expected as the result of the past conditions over a 

 considerable part of this area. The geological evidence indicates 

 that this part of India is one of the oldest of land-surfaces on 

 the globe. Ever since the East and West Cretaceous oceans 

 washed its shores, the fringing line of which is preserved at different 

 points, some part of it at least remained dry land. Very similar 

 conditions appear to have existed during Nummulitic times ; and not 

 until the advent of the Eocene does there appear to have been any 

 connection with Paloearctic lands and faunye on the north-west." 



What Blanford did for the distribution of the Indian vertebrate 

 fauna has to be done for the invertebrates ; and of these the 

 Mollusca can best be treated by themselves. The means of 

 migration of land-shells are limited and progress is slow ; it 

 is stopped abruptly by physical change of conditions. A forest 

 form cannot cross a hot sandy tract of even a few miles in width. 

 They are in a great measure attached to their habitat: they 

 would be less affected by terrestrial disturbances than vertebrates, 

 and survive changes which would destroy or drive out the latter. 



It is apparent that the distribution of the Land Mollusca does 

 not conform in every way with that of the Vertebrata ; in one sense 

 it is more intimately connected with physical features long since 

 vanished. This is shown in the south in Peninsular India, which is 

 undoubtedly a very ancient land -surf ace*. Again, in the north, 

 in Assam t, from the base of the Eastern Himalaya, the great 

 gneissic mass of Bhutan, the Aka and Dafla Hills, towards Brahma- 

 kund points to another ancient land, presumably so, for not far 

 distant were in succession the shores of the Cretaceous, of the 

 Nummulitic, and Tertiary seas. Earlier than these times the 

 present base of the mountain-range would appear to have been 

 near the northern deposition of the Gondwana Series, which is 

 found turned up and inverted by overthrust at its junction with 

 the gneissic rocks, with the Tertiaries on the south resting uncon- 

 formably on the Damudas J, a feature which, absent at intervals, 

 extends for some 350 miles between long. 86° 30' and long. 94° E. 

 This extension of the Gondwana system from the northern side 

 of Peninsular India, across the Gangetic plain to the eastward into 

 Assam, is the link which unites the two ancient land-areas §. 



Is it not something more than a mere accident that in Peninsular 

 India we find species belonging to genera peculiar and restricted to 

 that part of India, such SiS Ariophnnta, Eujjlecia, &c., and on reaching 

 the mountain-slopes of the Eastern Himalaya so many very peculiar 

 species and genera come in which have not been met with even in 



* Man. Geol. India, Medlicott & Blanford, 1879, p. 291. 

 t Man. Geol. India, Oldham, 1893, p. 488. 

 t J. A. S. B. vol. xliv. pt. 2, p. 35 (1875). 

 I Man. Geol. India, 1879, pp. 618-520. 



