FRESH-WATER FISHES OF SIAM, OR THAILAND 207 



The two known species may be distinguished as follows : 



la. Scales in lateral line 37 or 38 ; branched dorsal rays 9 or 10 burmanicus 



1&. Scales in lateral line 41 or 42 ; branched dorsal rays 11 or 12 acanthopteriis 



SCAPHIODONICHTHYS BURMANICUS Vinciguerra 



Scaphiodonichthys btirmunicus Vincigueeka, 1889-90, p. 285, pi. 11, fig. 11 

 (Burma). — Smith, 1933a, p. 79 (in part) (Northern Siam). 



This strongly marked species, which Dr. Vincigiierra described 

 from lower Burma near the Thai border in 1890, seems to have re- 

 mained vmnoticed by others until the writer reported it from Thailand 

 in 1933. Numerous specimens were obtained in Northwestern Thai- 

 land in December 1932 and January 1933 in the Mepai at and near 

 Muang Pai, in the Mekong Noi north of Mehongsorn, and in a brook 

 west of Mesarieng, all of these tributaries of the Salwin. Specimens 

 in the Deignan collection are from the Huey Mekong Klia, at the foot 

 of Doi Mekong Kha, between Mesarieng and the Salwin. The British 

 Musem contains specimens collected by Major Stockley on the boun- 

 dary between Thailand and Tenasserim. 



In Thailand this fish is restricted to mountain streams in the west- 

 ern drainage into Burma. The species is separated from the form in- 

 habiting the headwaters of the Meping and tributaries of the Me- 

 kong by high mountain ranges. This separation has permitted the 

 development of certain differential features, which are pointed out in 

 the account of the following species. 



A length slightly in excess of 18 cm. is attained. 



SCAPHIODONICHTHYS ACANTHOPTERUS (Fowler) 



Scaphiodonichthys burmanicus Smith, 1933a, p 79 (in part) (Northern Siaiu).— 

 FowLEB, a935a, p. 120 (Slian States and Northern Siam). 



ScapModontopsis acanthopterus Fowleb, 1934a, p. 119, figs. 74, 75 (Shan States, 

 Burma; Metang River, Chiengmai). 



A critical examination of an ample series of specimens indicates 

 that this species, known from the basins of the Meping in Thailand 

 and the Mekong in Thailand and the Shan States of Burma, is dis- 

 tinct from S. burmanicus (q. v.), known from the basin of the Salwin 

 in Thailand and Burma and from minor streams in Tenasserim. The 

 differences, while not marked, are constant and involve the number of 

 scales in the lateral line and the number of branched rays in the 

 dorsal fin. Thus, in jS. acanthopterus the lateral-line scales number 

 41 or 42 against 37 or 38 in S. turrnanicus, and the branched dorsal 

 rays are always 11 or 12 in the former species as against 9 or 10 in the 

 latter. Further comparison of specimens may bring out other 

 differences. 



The largest specimens examined from Thai waters have been 21 

 to 22 cm. long. 



