FRESH-WATER FISHES OF SIAM. OR THAILAND 357 



the Royal Forest Department of Siam at Maesort, on the Menam Muey, 

 a tributary of the Salwin, in Western Thailand, was identified and 

 recorded by the writer. This is the only Thailand specimen of which 

 he has knowledge, and it seems to be the one described and figured by 

 Hora (1937b), who concludes that the Thailand and Burmese forms, 

 while differing in some respects from the Indian, cannot, from the 

 material available, be separated therefrom as races or subspecies (vari- 

 ety huri7ianictLS of Day) . 



At Maesort the vernacular name applied to this fish is pla sawai nu^ 

 borne by related catfishes in other parts of Thailand. 



Genus PANGASIUS Cuvier and Valenciennes 



Pangasius Cuviee and Valenciennes, Histoire naturelle des poissons, vol. 15, 

 p. 45, 1S40. (Type, Pimclodus pangasius Hamilton.) 



This is the most numerous genus of Thailand catfishes. All the spe- 

 cies inhabit the larger rivers and some of them are amenable to pond 

 life. The principal differential characters are to be found in the denti- 

 tion, barbels, anal rays, and coloration. Two of the largest catfishes in 

 the world belong here. While all the species are carnivorous, some of 

 them thrive on fruit or aquatic vegetation, especially when loss or 

 atrophy of teeth necessitates abandonment of a predatory career. In 

 certain species the phenomenon of the partial or complete disappear- 

 ance of the teeth after a certain size or age is reached has been criti- 

 cally examined, and it is probable that one nominal genus {Pangasi- 

 anodon)^ based largely on the complete absence of teeth, represents 

 simply a normal age stage of a Pangasms. 



As all these fishes are of striking appearance and some of them have 

 come into local prominence because of their economic importance, it is 

 natural that they should have acquired many vernacular names in 

 different parts of their range. Some of the names, like j)la tepo and 

 ■pla tejya^ are applied to only a single species; others have come to be 

 used for groups of species of similar appearance, like pla sangkawad 

 and pJa smvai. For some individual species of wide distribution there 

 is a large number of local names. Finally, the same species may bear 

 different names in the same locality when young and when adult. 



The 15 local species, some peculiar to Thailand or to the boundary 

 waters of Thailand and Indo-China, and some of them known from 

 very scant material, may be identified as follows : 



la. Patches of vomerine teeth separated from each other but united with or 

 closely contiguous to palatine patches. 

 2a. A large black humeral spot always present; no black longitudinal band 

 along side ; each caudal lobe with or without a submarginal black longi- 

 tudinal band ; anal rays 28 to 33 — ---, — — - larnaudii^ 



590087—45 24 



