FRESH- WATER FISHES OF SUM, OR THAILAND 391 



insular Siam, shows almost perfect agreement, with the exception that 

 in the Burmese examples the top of the head and the scapular bone are 

 much more rugose (whereas, according to Bleeker, the opposite condi- 

 tion should exist) . 



As bearing further on the question of the specific identity of M. 

 cavasius and M. nig7'iceps, the writer received from J. R. Norman, in 

 charge of the fish collection in the British Museum, the following 

 letter, dated March 1, 1937 : 



On receipt of your letter I got out specimens of Macrones cavasius and M. 

 nigriceps and compared these carefully. I have no special knowledge of this 

 group of fishes and it is possible that somebody who knew them well might be 

 able to see minor points of difference. I am unable to detect any of importance 

 and am of the opinion that the two forms are identical. 



The fish Mystus rhegma Fowler, based on a single specimen 6.8 cm. 

 long, is believed to be the present species. The space between the 

 dorsal and adipose fins, the principal feature on which the species is 

 separated from M. nigriceps (Cuvier and Valenciennes), is somewhat 

 more than in average specimens but is thought by the present writer 

 to represent individual variation. The three indistinct dark longi- 

 tudinal bands on which stress is laid (although only two are men- 

 tioned in the description of the species) are characteristic of young 

 M. cavasius. Fowler (1935a) cites three specimens of M. nigriceps 

 with the "dorsal and adipose fins connected by a membrane," but his 

 figure of one of them shows the fins close together but unconnected, 

 and in the descriptions of the species by Weber and de Beaufort and 

 others these fins are referred to as contiguous but unconnected. 



This fish throughout its range in Thailand is known as pla kayeng, 

 sometimes shortened to pla yeng. In allusion to the very large adi- 

 pose fin of a translucent light green color, the fish in parts of the 

 Menam Chao Phya is called pla Jcayeng bai khao {bai khao, rice leaf). 



MYSTUS MICRACANTHUS (Bleeker) 



Bagrus micracanthus Bleekee, 1846 (3), p. 151 (Batavia). 



Hypselohagrus micracanthus Sauvage, 1881, p. 161 (Menam). 



Mystus micracantlms Fowler, 1934a, p. 94 (Chiengmai) ; 1934b, p. 337 (Ban 



Thung Luang); 1937, p. 146 (Kemarat). — Herre and Myers, 1937, p. 69 



(Singora).— FowLEB, 1939, p. 43 (Krabi). 



Until a comparatively recent date this species was known only from 

 rivers of Sumatra, Borneo, and Java. It was first detected in Thai- 

 land in 1927, when, on February 7, a specimen 8 cm. long was col- 

 lected in the Chantabun River, Southeastern region. In the next 

 year, on July 14, one 12.5 cm. long was obtained in the Tadi River, 

 Nakon Sritamarat, Peninsular Thailand. Fowler extended the range 

 to the Meping (Northern area) and the Mekong (Eastern region). 



