FRESH-WATER FISHES OF SIAM, OR THAILAND 371 



scribes the palatine as well as the vomerine teeth. Hora has appar- 

 ently misread Sauvage, who refers to the variation in the vomerine 

 teeth dependent on age, and the entire absence of vomerine teeth in a 

 specimen 75 cm. long and the complete disappearance of vomerine as 

 well as maxillary teeth in specimens a meter long. The absence of 

 palatine teeth in a specimen of H. hypophthalmus, 14.5 cm. long, from 

 Bangkok, was suggested by Hora as explainable by Sauvage's state- 

 ment, which may properly be quoted in full : 



In this species tlie length of the barbels and the arrangement of the vomerine 

 teeth vary much with age, a fact interesting to note, since one knows that 

 these two characters, which from this very reason have no value, have been 

 regarded as specific by the generality of ichthyologists. 



In an individual of middle age (60 cm. long), the maxillary barbel extends to 

 the edge of the preopercle; the mental barbel, a fourth as long as the head, 

 reaches the level of the anterior edge of the orbit. The vomerine teeth are dis- 

 posed in two very straight bands separated from each other by a space equal to 

 their length. 



The barbels are a little shorter in an individual 65 cm. long; the barbels are 

 shortened further in an example of 75 cm., in which the maxillary barbel 

 reaches only to the level of the center of the eye and has the same length as the 

 mental barbel. The vomerine teeth are absent. 



The maxillary teeth, as well as the teeth of the vomer, disappear at the size 

 of 1 meter ; there is no mental barbel, the maxillary barbel is only 1.5 cm. long. 



HELICOPHAGUS WAANDERSII Bleeker 



HelicopJiagus waandersii Blebkee, 1858 (189a), p. 175 (Palembang, Sumatra). 

 Helicophagus waandersi Hora, 1937d, p. 236 (Siam). 



As far as collected specimens indicate, this fish of the Smnatran 

 rivers is confined in Thailand to the basin of the Menam Chao Phya. 

 It is common at times in the Bangkam River at Lopburi, in the Chao 

 Chet River, and in parts of the Chao Phya proper, A specimen from 

 the Menam Chao Phya is in the British Museum. 



An interesting record for this species was the capture of a specimen 

 18 cm. long, in a trap in the Gulf of Siam far off the mouth of the 

 Menam Chao Phya, August 12, 1923. A great volume of fresh water 

 was at that time pouring out of the large rivers of Central Thailand, 

 and the salinity of the upper gulf was materially reduced. 



In Sumatra a length of 34 cm. is reported. In Thailand the largest 

 specimen, taken at Nakon Sawan January 5, 1925, was 31.5 cm. long. 



The fish makes a grunting sound, noticed especially when being 

 taken into one's hand from out of the water. In allusion to the shape 

 of the head, it is given the name pZa nu {nu, mouse) by Thai fisher- 

 men, this term being used also as a suffix to names borne bj^ various 

 species of Pangasius. 



