128 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 

 MYSTACOLEUCUS ARGENTEUS (Day) 



Acanthonotus argenteus Day, 1888, p. 807 (Tenasserim). (After Tickell's MS.) 

 Matsya urgcntai Day, 1889, p. 293, fig. 102 (Tenasserim). (New generic name.) 

 Mystacoleucus aryenteus Smith, 1933a, p. 79 (Salwin and tributaries in Siam 

 and Burma).— HoRA, 1939, p. 401, fig. (Burma). 



Under the manuscript name Acanthonotus argenteus of Tickell, 

 Day (1888) published a description of a small cyprinoid fish (largest 

 5.4 inches) said by Tickell to be "very common in the streams of the 

 interior of the Tenasserim district" of Burma. As the generic name 

 Acanthonotus had been thrice preoccupied in ichthyology, Day later 

 established the genus Matsya for the accommodation of the fish that 

 for many years was known as Matsya argentea. The genus Matsya 

 was inadequately characterized, the chief distinctive feature being a 

 small forwardly directed spine anterior to the dorsal fin; but from 

 the description and figure of the species it appears that the dorsal 

 fin had 8 branched rays preceded by a single strong serrated spine, 

 the anal fin had 7 simple and branched rays, there were 30 scales in 

 the lateral line, no barbels were referred to in the text or shown in 

 the figure (although barbels were subsequently shown to be present), 

 and the brilliant silvery of the body and head was relieved by lilac 

 and blue shades and a tinge of olive-yellow on the back, with the 

 dorsal fin orange-scarlet, its edge bordered with black except on the 

 last two rays, the other fins lemon-yellow. 



A series of nine specimens in the U. S. National Museum were col- 

 lected by Deignan at Ta Ta Fang in October 1936. These are 6.9 to 

 8.2 cm. long. The tube-bearing scales in the lateral line are 33 to 

 35, the scales in the transverse line from the midline of the back to 

 the base of the ventral fins are 7.5-1-3 or 3.5, the predorsal scales are 12 

 or 13, and the circumpeduncular scales are 16; the dorsal rays are 

 ii,8 or iii,8, with the last simple ray osseous and strongly denticulated, 

 and the anal rays are ii,6; the rostral barbels are somewhat shorter 

 than the maxillary and both are shorter than the eye; the sharply 

 defined jet-black margin of the dorsal fin becomes very narrow or may 

 be practically deficient at the last two rays. A specimen from Huey 

 Mekong Kha, a brook tributary to the Salwin west of Mesarieng, 

 Western Thailand, is 10.5 cm, long and is a female with well-ripened 

 eggs. 



Day does not appear to have seen the fish, the Indian Museum and 

 the British Museum had no specimens, and the species remained 

 something of an ichthyological mystery until many specimens col- 

 lected by H. G. Deignan and the writer in the Salwin and its tribu- 

 taries in Thailand and Burma in 1932, 1933, and 1936 proved to be 

 Day's species. 



