102 Contributions to Indian Malacology.. [No. 2, 



238, &c. y which calls for a few remarks. Although I differ in many 

 points from Mr. Theobald's views as put forward in this paper and in 

 the earlier one of 1863, especially those on the origin, migration, and 

 distribution of specific forms, I see no object to be attained in answer- 

 ing at length opinions long since refuted, as I believe, by far more 

 competent authorities and far abler writers. The works of Edward 

 Forbes, Owen, Lyell and a host of others besides Darwin, will serve to 

 shew the arguments relied upon by the great majority of living natur- 

 alists, to prove the doctrine of " specific centres," that is the theory 

 that all members of the same species, whether existing or dead, have 

 descended, not necessarily from one pair, but from one parent stock, 

 living in one spot. To call this, however, the Darwinian theory, as 

 Mr. Theobald appears to do, would be paralleled by calling the 

 earth's rotation round the sun the Newtonian 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 the planets 

 around the sun. 



If I refer briefly to one remark of Mr. Theobald's, (that in his first 

 paper, J. A. S. B. for 1863, Vol. XXXII. p. 376) it is because it 

 appears to me the only argument of any importance which he has 

 advanced in favour of his opinions. The question of the distribution 

 of fresh water shells and especially of the bivalves, with their limited 

 powers of progression, is a well worn argument in favor of the 

 sporadic origin of species ; that is, of the descent of each species from 

 many parent stocks, existing in distinct and separate localities. But 

 if all the facts of the case are fairly stated, there appears much, even 

 in this instance, in favour of the doctrine of specific centres. The 

 facts are briefly these. Many species of. Unio, e. g. U. marginalis, 

 Lam. exist throughout a large tract of country, in almost every river 

 and stream, and even in many ponds and marshes, although these 

 rivers, &c. have no fresh water communication with each other what- 

 ever, and the animal is incapable of living in the sea, or of traversing 

 the land. On the other hand, tfie area inhabited by this species is 

 continuous ; that is to say, the same species does not occur in tropical 

 Asia and tropical America, for instance. Other species are restricted 



