xiv Re'port on the Zoological Survey of India 



of distribution for both, beetles and arachnids. So far as taxonomy is 

 concerned he has shown that great individual variation takes place 

 in certain species and that many forms hitherto regarded as specifically 

 distinct must be united. On the other hand he has described a number 

 of new species and several new genera. The large number of indivi- 

 duals examined gives peculiar weight to his taxonomic views. 



Survey o£ the Freshwater Molluscs of India and of their Trematode 

 Parasites. — In the section of this re^^ort that deals with touring 

 and field-work I have already said a good deal about this survey. 

 Here I may add a few words as to the zoological results already 

 achieved. Although the work of the older Indian conchologists, 

 especially of Benson, Stoliczka, Theobald, CI. Nevil], and W.T. Blan- 

 ford, was extremely valuable and in many districts in a sense practi- 

 cally exhaustive so far as the aquatic species were concerned, their 

 descriptions of those species were unfortunately for the most part far 

 too short, as was customary at the time. As a rule (except Stoliczka) 

 they paid little attention to anatomy and gave few details as to 

 habitat or habits. It has been our endeavour to make good these 

 deficiences. We have examined by far the greater part of the fresh- 

 water Gastropods of India proper, of Baluchistan, and of those parts 

 of Assam and Burma we have been able to visit, in a living condition. 

 We have dissected large numbers of species and examined the radula 

 and operculum of still more. Our field-books contain notes as to the 

 precise conditions in which our specimens of each species were found. 

 In short, we are now in a position to commence concerted work on a 

 comprehensive monograph of the Indian forms. In the meanwhile a 

 series of more or less detailed papers dealing with special districts or 

 with special points in taxonomy, etc., are being published in the Records 

 of the Indian Museum. A paper on the geographical distribution of 

 the freshwater Gastropods and its direct bearing on that of human 

 disease was read before the medical section of the Science Congress at 

 Nagpur. So far as the bivalve molluscs are concerned Dr. Baini Prashad, 

 while still attached to tbe Fishery Department of Bengal, Bihar and 

 Orissa, has revised most of the Indian genera of Unionidae on an 

 anatomical basis. The number of new species of aquatic molluscs found 

 in India proper has been small, but that of nominal species which it is 

 possible to link together by examining sufficient specimens, large. 



The investigation of the cercarise found in the Indian Mollusca was 

 commenced by Dr. S. W. Kemp, with the assistance of Dr. F. H. 

 Gravely in certain particulars. They published a preliminary account 

 of the results of infection experiments in Vol. VII of the Journal of 

 Indian Medical Research, with an elaborate precis of the literature on 

 the biological aspect of Schistosomiasis available at the date at which 

 their paper was written. Dr. Kemp was, towever, obliged to go to 

 Europe before his investigations on the anatomy and taxonomy of the 

 cercarise, which can only be studied satisfactorily in a living condition, 

 were far advanced, and the work was taken on with great enthusiasm 

 by Major R. B. Seymour Sewell, who has prepared detailed descriptions 

 and very beautiful drawings of over fifty species found in water-snails 

 from different parts of India. It is hoped that the medical authorities 



