FRESH-WATER FISHES OF SIAM, OR THAILAND 87 



rear its confluence with the Chao Phya at Paknampo; in the Pasak 

 Ki ver both above and below the barrage at Dha Luang ; in the Nakon 

 Nay ok River; and at various places in the Meklong. It also frequents 

 the larger canals. 



The maximum size represented in the collections and records of the 

 Thailand Fishery Service was 23.5 cm. over all, 20.5 cm. to the base 

 of the caudal fin. This was a specimen taken February 27, 1925, in 

 the Pasak River at Dha Luang. Fish 14 to 20 cm. long are common. 



The fish may be rated as common to abundant. It often goes in 

 scattered schools, and when it comes to the surface may be readily 

 recognized by the narrow black margin of the posterior border of the 

 caudal fin. 



G. siamensis is the genotype of Cultrops. The species was described 

 in detail by Hora, and a good figure was given by him. Among the 

 outstanding features are the strongly compressed body and head, 

 nearly straight and horizontal dorsal profile, trenchant abdominal 

 edge, subvertical mouth, strongly developed symphyseal hook on the 

 lower jaw and correspondingly deep emargination on the upper jaw, 

 triserial pharyngeal teeth (4, 4, 2), long setiform gill rakers number- 

 ing 23 to 26 on the lower arm of the first arch, tripartite natatory 

 vesicle, small scales (about 90 in lateral series, 12 to 15 above lateral 

 line, 5 to 7 between line and base of ventral fin, 55 to 60 predorsal), 

 lateral line often (perhaps usually) consisting of 2 or 3 disconnected 

 and overlapping parts, dorsal fin inserted over the space between the 

 ventral and aiial fins and consisting of 7 branched rays and 2 slender 

 nonosseous simple rays, and long anal fin with 23 to 25 branched rays. 



In the arrangement of three overlapping lateral lines, as exhibited 

 by the type, the uppermost section beginning at the upper angle of the 

 gill opening may extend over 20 to 30 scales to a point in advance of 

 or over the base of the ventral fins ; the middle section, the shortest, 

 may cover 18 to 20 scales, beginning over the middle of the pectoral 

 fin and extending to the ventral, the anterior 15 scales overlapped by 

 the uppermost section ; the lowermost section, always the longest, be- 

 gins over the pectoral fin and extends to the base of the caudal fin, its 

 anterior 10 to 15 scales overlapped by the uppermost section. 



As jjointed out by Hora (1923b) in the first account of Gutter siamen- 

 sis, his single specimen, 17.5 cm. long, without caudal fin differed in 

 several important features from the generally recognized definition 

 of GuUer, and he suggested that the differences were sufficient to dis- 

 tinguish the new species generically from Gulter. At that time he 

 was dissuaded from establishing a new genus because of the paucity of 

 material for the study of individual variation. 



It is believed that Gulter wolfii will prove to be this species. In 

 squamation, gill rakers, teeth, fin rays, and other features there is 



