358 BULLETIN 18 8, UNITED STATES NATIONAL MUSEUM 



2&. No black humeral spot. 



3a. A single broad black longitudinal band on side ; caudal lobes plain ; anal 



rays 36 to 40 pleurotaenius 



36. Several broad black longitudinal bands on side ; caudal lobes blackish, 



with pale edge; anal rays 34 to 36 sutchi 



1&. Vomerine teeth united into a single quadrate patch, with a patch of palatine 

 teeth on each side close to but not joined to vomerines. 

 4a. Patch of vomerine teeth about 3 times as wide as its antero-posterior diam- 

 eter ; patches of palatine teeth extending outward and backward from 

 side of vomerine patch ; anal rays 29 to 31. 

 5a. Caudal peduncle long and slender, its least depth contained 2.5 to 3 times 

 in its length ; maxillary barbels reaching pectoral fins, 0.65 to 0.75 length 

 of head; head moderately depressed; snout very long; eyes entirely 



above level of mouth; first dorsal ray shorter than head nasutus 



56. Caudal peduncle short, its least depth less than 0.5 its length ; maxillary 

 barbels reaching opercles, less than 0.5 length of head ; head very broad 

 and depressed, snout short ; eyes partly below level of mouth ; first 



dorsal ray longer than head beani 



46. "Vomerine teeth in a large quadrate patch, its antero-posterior diameter 0.7 

 to 0.8 its width ; patches of palatine teeth small and closely applied to the 



outer sides of the vomerine patch, anal rays 35 to 40 polyuranodon 



Ic. Vomero-palatine teeth in a single fully united crescentic patch; anterior dor- 

 sal, ventral, and pectoral rays produced into long filaments ; a conspicuous 



white humeral spot. Size large. Menam Chao Phya basin sanltwongsei 



Id. Vomero-palatine teeth in 4 separate patches that are (1) regularly crescentic 

 in shape or (2) with the palatine perpendicular to the vomerines. 

 6a. Palatine patches of teeth more or less at right angles to vomerine patches; 



maxillary barbels less than 0.5 length of head ; anal rays 42 f owleri 



66. Palatine patches of teeth forming a crescentic band with vomerines. 



7a. Maxillary and mandibulary barbels shorter than head ; anal rays 28 to 34. 



8a, Maxillary barbels less than 0.5 length of head ; mandibulary barbels 



less than 0.25 length of head ; distal part of dorsal, caudal, and 



pectoral fins blackish micronemiis 



86. Maxillary barbels more than 0.5 length of head and extending to base 

 of pectoral fins. 

 9a. Mandibulary barbels not exceeding 0.5 length of head ; anal rays 



31 to 34 ; coloration of caudal fin plain pangasius 



96. Mandibulary barbels more than 0.5 length of head ; anal rays 28 

 or 29 ; caudal fin with well-defined dark subniarginal band in 



each lobe taeniurus 



76. Maxillary barbels longer than head; mandibulary barbels equal to or 

 longer than head ; anal rays 30 to 44. 

 10a. Maxillary barbels extending to middle or tip of pectoral fins or to 

 base of ventral fins ; anal rays 29 to 36. 

 lie. A large round blackish spot on opercle; vomero-palatine teeth in 



4 round equal patches; anal rays 33 or 34 aequilabialis 



116. No large dark spot on opercle ; patches of vomerine and palatine 

 teeth of dissimilar shape and size. 



12a. Anal rays 30 or 31 niacronemus 



126. Anal rays 33 to 36 siamensis 



106. Maxillary barbels extending beyond origin of anal fin ; anal rays 

 42 to 44 long'ibarbis 



