FRESH-WATER FISHES OF SIAM, OR THAILAND 11 



Sunda River, its bank being at the level of the present 100-meter iso- 

 bath. Between these two great rivers was an extensive plain from 

 which rose a few isolated mountains less than 200 meters in height. 

 The writers pointed out : 



It will be quite apparent that interchanges of freshwater fauna between the 

 two hydrographic systems would be very easy or rather that there was only one 

 and the same fauna common to all this immense region. * * * 



The practical identity of ichthyologic fauna in countries now separated by the 

 sea, is easily understood when the geologic history of the area is known. Recrea- 

 tion in thought of the great continental block joining these countries as it 

 appeared before its immersion, with its two great rivers, provides at once the 

 key to the common origin of the fauna. 



In a table showing "distribution of the freshwater fishes of southern 

 Asia," Krempf and Chevey listed species of the East Indies, Indo- 

 China, Burma, and India but made no mention of Siam and Malaya, 

 which, inferentially, are included under Indo-China; certain species 

 are shown thereunder that are Imown only from Siam. The table, 

 while fully illustrating the great similarity between the fishes of Indo- 

 China and the East Indies, loses some of its force by incompleteness 

 and errors. Only 76 species of fishes common to Indo-China (and 

 Siam) and the East Indies are shown. The list could be doubled, and 

 about 40 cyprinoid species alone are omitted. Among the errors are 

 the inclusion under the East Indies of genera and species peculiar to 

 Siam and Indo-China (e. g., the cyprinoid Puntioplites froctozysron) ^ 

 the omission from the East Indian list of common species found there 

 as well as Indo-China (e. g., the catfish Wallago dinema) , and the non- 

 listing of various species of Indo-China (and Siam) that are known 

 also from Burma and India (e. g., the catfish Glarias 'batrachm) . 



In the foregoing conception, the fresh-water fish fauna of the East 

 Indies, Indo-China, Malay Peninsula, and Siam had a common origm. 

 The general subject is discussed at some length b}'- Hora (1937a) with 

 special reference to India ; but inasmuch as his observations and con- 

 clusions have a more or less direct application to Siam, they are quoted 

 directly : 



The relationships and the geographical distribution of the freshwater fishes 

 of India were discussed by two of the leading ichthyologists, Day and Giinther, 

 of the last century. The former advocated Malayan affinities for the Indian 

 fauna, while the latter, though admitting the migration of several Oriental 

 freshwater fishes to Africa, laid special stress on the African affinities of this 

 fauna. Beyond some casual references very little work has since been done on 

 this aspect of the Indian freshwater fishes, and in view of the advances that have 

 been made in our knowledge of the paleogeography and systematics of fishes 

 it seems opportune to review the whole subject in the light of recently discov- 

 ered facts. 



* * * 



There is an unfortunate impression, mainly among geologists, that in the 

 case of fishes dispersal may be effected through the agency of birds, chiefly 



