130 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 

 MYSTACOLEUCUS MARGINATUS (Cuvicr and Valenciennes) 



Barhus marginatus Cuvieb and Valenciennes, 1842, vol. 16, p. 164 (Tjicanigui 



River and Sijira, Java). 

 Mijstacoleucus marginatus Smith, 1931d, p. 185 (Siam generally). — Fowlee, 



1934a, p. 115 (Chiengmai) ; 1934b, p. 342 (Ban Thnng Luang) ; 1935a, p. 114 



(Srisawat, Khao Nam Poo) ; 1937, p. 176 (Mepoon, Kemarat) ; 1939, pp. 41, 



68 (HueyTang, Trang). 



This species, known from Java, Borneo, Sumatra, and Malaya, has 

 a wide distribution in Thailand. In the basin of the Menam Chao 

 Phya, no specimens appear to have been obtained south of Paknampo. 

 It has been found in the upper part of the Menam Nan ; in the Mewang 

 at Lampang and in the Mesoi, a tributary of the Mewang ; and in the 

 Meping and a number of its tributaries, including the Mekham. In 

 the Meklong the species is known from both branches, the Kwe Yai 

 at Kanburi and the Kwe Noi at Saiyok. In Peninsular Thailand, the 

 fish has been ascertained to inhabit the Tapi River near Bandon; 

 various streams at or near the towns of Nakon Sritamarat and Ron- 

 pibun; a small hill stream near Patalung; and the Patina River, a 

 specimen from the last, collected by Annandale and Robinson, being 

 in the British Museum (listed as Barbus obtusirostris) . 



The fish was first found to be an inhabitant of the Mekong Basin by 

 the taking of specimens in the Mekok at Chiengrai in March 1924. 

 On February 16, 1929, a specimen was collected at Pong, on the Nam 

 Pong, a branch of the Nam Chi, which, in turn, flows into the Menam 

 Mun, the principal tributary of the Mekong in Thailand. At Pak- 

 jong, on headwaters of the Menam Mun, a specimen obtained on June 

 21, 1934, was typical except for the absence of rostral barbels. More 

 recently Fowler reported it from the Mekong itself at Kemarat, East- 

 ern Thailand, and from the Peninsular region in Huey Yang and in 

 the Trang waterfall stream. 



The largest example met with in local waters was 20 cm. long, 

 taken in Klong Tadi, Nakon Sritamarat. Full maturity is attained 

 at half that size. Examples over 17 cm. long are uncommon. 



The development of the barbels varies with size, sex, and other con- 

 ditions. The maxillary barbels are usually about twice the length 

 of the rostral, and may equal the diameter of the eye or be only one- 

 third that size. Of two specimens from the headwaters of the Menam 

 Nan at Muang Ngop, April 23, 1936, one, a male 10.5 cm. long, had 

 maxillary barbels one-third the diameter of the eye ; the other, a female 

 14.2 cm. long with well-developed ova, had maxillary barbels two- 

 thirds the diameter of the eye. In five specimens 6.3 to 7.6 cm. long 

 from the Menam Nan, March 31, 1936, these barbels are half the 

 diameter of the eye, while in various specimens 9.3 to 12 cm. long from 

 the Mekok in July and August the maxillary barbels equal the diameter 

 of the eye. 



