1865.] Proceedings of the Asiatic Society. 73 



he was in reality only opposing the doctrine of specific centres, which 

 had been established by Edward Forbes, Owen, Lyell and many 

 others, and accepted by the great majority of living naturalists. To 

 call this the Darwinian theory, as Mr. Theobald appeared to do, would 

 be paralleled by calling the earth's rotation round the sun the New- 

 tonian theory. In each case the earlier theory is only a necessary step 

 in the line of argument, and the hypothesis of the origin of species by 

 means of natural selection is no more involved in the doctrine of 

 specific centres, than was the theory of universal gravitation in that of 

 the rotation of planets round the sun. 



" Adverting then to the distribution of fresh water mollusca, which 

 Mr. Theobald had advanced in favour of his opinion, and especially of 

 the bivalves with their limited powers of progression, a well worn 

 argument in favour of the sporadic origin of species, i. e. of the 

 descent of each species from many parent stocks, existing in distinct 

 localities, the author pointed out that there appears much, even in this 

 instance, in favour of specific centres. Widely distributed species, such 

 as Unio marginalis, although found in rivers, tanks, &c, which have 

 no communication with each other, are continuously distributed with 

 respect to geographical area, i. e. the same species do not occur, e. g. 

 in tropical Asia and tropical America. Other species, e. g. Unio 

 olivaceus, c%c, are restricted to a single river, and in other cases again, 

 such as Unio ceruleus, &c, and its allies, one form is found over a 

 considerable area in Bengal, and in separate rivers, and is replaced at 

 a distance, as in Sind and Western India, by forms which may either 

 be considered as distinct species or as local varieties, according to the 

 value attached to specific rank. In the intermediate country of Central 

 India, we find intermediate forms. The case of fresh water mollusca 

 is quite an exceptional one, and it was certainly more philosophical to 

 consider that our knowledge of the means of distribution in this case 

 is imperfect, than to arrogate to ourselves complete knowledge of the 

 subject, and to assert that no means of passage exist." 



Referring to the latter part of the above paper, Mr. H. F. Blanford 

 mentioned some facts of the distribution of the fresh water genera 

 Melania, Paludomus and their allies which in connection with an 

 observation of Mr. Darwin's seemed to account, in part at least, for the 

 distribution of fresh water mollusca. Mr. Darwin had found the seeds 



