372 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



Genus LAIDES Jordan 



Laides Joeoan, Genera of fishes, pt. 3, p. 293, 1919. (Type, Pangasius hexanema 

 Bleeker. ) 



In establishing a genus to accommodate the single known species, 

 Bleeker in 1858 gave it the Sundanese name of Lais, by which the fish 

 was known for many years. This name was preoccupied in tunicates 

 (Gistel, 1849) and Jordan in 1919 substituted the new name Laides. 



LAIDES HEXANEMA (Bleeker) 



Pangasius hexanema Bleeker, 1852 (67), p. 588 (Paleiubang, Batavia, Sumatra). 

 Lais hexanema Smith, 1931d, p. 179 (Nakon Nayok River). 



Previously known only from Java, Borneo, Sumatra, and Malacca, 

 this fish has been found to be of wide distribution in Thailand but 

 apparently is very uncommon. It was added to the local fauna in 1929 

 when a specimen 12.5 cm. long was collected by the writer at Pong, on 

 the Pong River, a tributary of the Menam Mun in Eastern Thailand. 

 A second specimen 13 cm. long was taken by a Boy Scout in the Nakon 

 Nayok River in 1930. The third and only other known specimen came 

 from the rapids of the Meping in Northern Thailand in December 

 1935; it is 12.5 cm. long and was obtained by H. G. Deignan from a 

 fisherman. 



This is an easily recognized catfish. There are 4 large, flat barbels on 

 the lower jaw and 2 long, ribbonlike maxillary barbels which extend 

 to the ventral fins or even beyond the first third of the anal fin; the 

 posterior nostrils are wide transverse slits on the upper surface of the 

 snout; there are no palatine teeth, and the vomerine teeth are in two 

 distinct transverse patches. 



On the Pong River this fish has the distinctive name of pla yom, 

 On the Nakon Nayok it is apparently not distinguished from other 

 small pangasiids and is called pla sangkaioart or sangkawad. 



Genus PANGASIANODON Chevey 



PangasUtnodon Chevey, Bull. Soc. Zool. France, vol. 55, pp. 53(}-542, fig. 1, pi. 1, 

 1930. (Type, Pangasianodon gigas Chevey.) 



In appraising the special features on which the genus Pangasianodon 

 is based, one may note that no examples of small or even medium size 

 have ever been described. Chevey did not designate a type specimen ; 

 the only example of which he gave the length was one of almost 2 

 meters, which he saw in August 1930. The detailed measurements that 

 accompany his description of P. gigas were taken from a model of a 

 fish, 2.5 meters long, in the Economic Museum of Cambodia, Avhich the 

 present writer has examined. 



In view of the well-established fact that in certain species of Pan- 

 gasius the teeth may disappear with age, the question naturally arises 

 whether in Pangasianodon the absence of teeth may not be simply an 



