FRESH-WATER FISHES OF SIAM, OR THAILAND 13 



these drainage systems. While the present watersheds would not per- 

 mit the passage of fishes from one to another, it is apparent that at 

 no very distant geological period physical barriers were not insur- 

 mountable and that fish populations now cut off from one another 

 had the opportunity to mingle. 



While Thailand has a very large percentage of species identical with 

 forms known also from Sumatra, Borneo, Java, and other East In- 

 dian islands, there is a considerable number of striking Siamese genera 

 of both the plains rivers and the mountain streams that are wholly 

 unrepresented in the Indo-Australian Archipelago. Among these 

 are the cyprinoid genera Aspidoparia, Bariliits, Catlocarpio, Cirrhinus, 

 Oreichthys, Probarhus, Punfioplites, Scaphiodonichthys, Scaphog- 

 nathops^ and Xenocheilichthys and the siluroid genera Amblyceps. 

 Heterohagrus^ and Oreoglanis. 



ZOOGEOGRAPHIC DIVISIONS OF THAILAND AND THEIR PRINCIPAL 



FRESH WATERS 



C. Boden Kloss (1915) proposed for Siam certain divisions in order 

 to afford to naturalists and others a better understanding of the zoology 

 and to avoid confusion in the recording of information. The divi- 

 sions suggested — Northern, Central, Western, Peninsular, Eastern, 

 and Southeastern Siam — may be convenient in the consideration of the 

 distribution of land animals but they are not always applicable to 

 fishes, for which the logical division of the country would be into 

 river basins or drainage systems. It happens, however, that the 

 Central, Peninsular, Eastern, and Southeastern divisions proposed by 

 Kloss may in general be accepted for fishes, leaving the limitations 

 of Northern and Western Siam subject to modification. 



Northern Siam has been defined as all that part of the country 

 lying north of latitude 17°5()'. It is mostly mountainous and forested 

 and is drained by three great rivers, the Salwin or Menam Kong, 

 the Menam Chao Phya (through its tributaries the Meping and the 

 Menan), and the Mekong. 



The northwestern corner of Northern Thailand is drained mostly 

 by the ]\Ienam Pai, which enters the Salwin soon after receiving the 

 Menam Surin as its chief affluent. Farther south another tributary 

 of the Salwin, the Menam Mue or Thaungyin, has as its principal afflu- 

 ent the Menam Yuam, an important stream with a generally southern 

 course. The Salwin and the Menam Mue constitute the Thailand- 

 Burmese boundary for upward of 300 kilometers. The part of Siam 

 drained by the Menam Mue may properly be treated as Northern Siam, 

 although classed as Western Siam by Kloss, who defined this division 

 as including all that area lying between the mouth of the Menam Mue 

 on the north and Koh Lak on the south and between the Tenasserim 



