FRESH-WATER FISHES OF SIAM, OR THAILAND 283 



GYRINOCHEILUS AYMONIERI (Tirant) 



Psilorhynchus aymonieri Tibant, 1883, p. 35 (new pagination) (Samrong-Tong 



Mountains, near Phnom-Penh, Cambodia). 

 Gyrinochcilus atjmonieri Hoka, 1935, p. 459, figs. (Cambodia, Slam). 

 Gyrinocheilus kaznakovi Bebg, 1906, pp. 306, 365 (Pailin). — Smith, 1931d, p. 187 



(Siam generally). — Fowler, 1934a, p. 137 (Cbiengmai, Metang River). 

 Gyrinochcihis kaznakoi Hoka, 1923b, p. 159, fig., pi. 12, figs. 4-7 (Nontaburi, 



Pailin). 

 Gyrinocheilops kaznakoi Fowr.EE, 1937, p. IGO, fig. 96 (Paknam, Tachin) ; 1939, 



p. 74 (Trang). 



This species has been found to have a very wide distribution in 

 Thailand. Specimens have been examined from the Menam Chao 

 Phya at Nontaburi and Paknam, Central Thailand ; from Bung Bora- 

 pet and various outlets of that swamp, Central Thailand; from 

 streams entering the Menam Sak from the east. Central Thailand; 

 from headwaters of the Menam Mun near Pakjong and from the 

 Menam Pong, tributary of the Menam Mun, Eastern Thailand ; from 

 the Meklong at Potaram and from the west branch of the Meklong 

 above Kanburi, Central district; from upper waters of the Menam 

 Nan, Northern region; from the Meping at Chomtong and from the 

 Mewang, Mekhan, and Mechem, tributaries of the Meping, Northern 

 area ; and from the Menam Tapi and other streams in the Peninsula. 

 The extension of the range farther south in the peninsula has been 

 recorded by Fowler (1939) from a waterfall stream near Trang. 



The fish is as yet unknown, and may be absent, from the South- 

 eastern region (as now limited) and from the basins of the Salwin 

 and other streams tributary to the Bay of Bengal in Northern and 

 Western Thailand. 



The remarkable modification in the branchial apertures in this 

 species is no doubt typical of the family. The usual exhalent open- 

 ing, closed by a broad membranous flap, is confined mostly to the side 

 above the pectoral base ; a portion extends for a short distance on the 

 broad ventral surface immediately in front of the pectoral. Above 

 the exhalent slit is a deep, narrow, vertical inhalent opening which 

 communicates with the mouth cavity in front of the gills. This 

 opening, whose vertical dimension exceeds the diameter of the eye, 

 is closed by a delicate velum attached along the anterior wall, while 

 the free upper end of the opercular flap extends along the posterior 

 wall of the lower third of the slit. 



The quantity of water that may enter the inhalent openings is 

 small; and in order that sufficient oxygen-bearing water may reach 

 the gills the respiratory movements are extremely rapid. Observa- 

 tions made on fishes up to 12 cm. long that had been in a large aquar- 

 ium for 2 years and were still perfectly sound showed a respiratory 



