i 



FEESH-WATER FISHES OF SIAM, OR THAILAND 355 



la. Four pairs of barbels (nasal, maxillary, mandibulary, and mental). 

 2a. Cleft of mouth not extending under eye; vomero-palatine teeth in a cres- 

 centic band which is divided or constricted into several parts ; air 

 bladder large, dorsoventrally flattened, free and closely applied to 



dorsal wall of abdomen Platytropius 



2&. Cleft of mouth extending under eye; vomero-palatine teeth in an unin- 

 terrupted crescentic band produced backward at sides ; air bladder small, 



tubiform, partly enclosed in bone Eutropiichthys 



1&. Two or three pairs of barbels (nasal barbels absent). 

 3a. Two pairs of barbels (maxillary and mandibulary). 



4a. Vomerine and palatine teeth present, these and jaw teeth disappearing 

 with age in some species; posterior nostril nearer to anterior nostril 

 than to eye and above a line from anterior nostril to upper edge of 

 eye ; eye more or less in line with a horizontal through angle of mouth. 



5o. Abdomen rounded Pangasius 



56. Abdomen cultrate Pteropangasius 



46. Vomerine teeth present, palatine teeth absent ; posterior nostril about 

 midway between anterior nostril and eye and in line from anterior 

 nostril to upper edge of eye ; eye above a horizontal through angle 



of mouth Helicophagus 



36. Three pairs of barbels (maxillary, mandibulary, and mental) ; vomerine 



teeth in 2 separate transverse bands Laides 



Ic. One pair of barbels (maxillary) ; eye below level of angle of mouth; teeth 

 entirely absent. Size colossal. Mekong basin Pangasianodon 



Genus PLATYTROPIUS Hora 



Platytropius Hora, .Tourn. Siam Soc, Nat. Hist. Suppl., vol. 11, p. 39, 1937. 



Platytropius is separated from PseuAeutropius chiefly on the char- 

 acter of the vomero-palatine teeth and the shape of the air bladder. 

 In Pseudeutropius^ with one species in Sumatra and several in India, 

 the vomero-palatine teeth are in a single continuous band while in 

 Platytropius these teeth are in distant patches that form a lunate band 

 constricted or divided in the median line and divided or constricted 

 into two, exceptionally three, parts on each side. The air bladder in 

 Pseudeutropius is thin walled and comes in contact with the abdom- 

 inal parietes above each pectoral fin, resulting in the formation of a 

 translucent area, while in Platytropius the organ is thick walled, dor- 

 soventrally flattened, and throughout lies close to the dorsal wall of 

 the abdominal cavity. 



PLATYTROPIUS SIAMENSIS (Sanvage) 

 FlGUBE 80 



Pseudeutropius siamensis Saxtvagb, 1883b, p. 154 (Menam Chao Phya). — Smith, 



1934b, p. 297 (Menam Chao Phya, Menam Nakon Nayok). 

 Platytropius siamensis Hora. 19.57a, p. 352 (Siam). — Hora, 1937c, p. 39, figs. 1, 



2, pi. 11 (with 4 figures) (Siam). 

 Nemasiluroides furcatus Fowijeb, 1937, p. 137, figs. lG-19 (Bangkok). 

 Pseudeutropius taakree {non Sykes) Smith, 1934b, p. 297 (Menam Chao Phya). 



In 1883 Sauvage described Pseudeutropius siamensis from a spec- 

 imen, 13.5 cm. long, collected by Dr. Harmand in the Menam Chao 



