390 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



frequents rivers, canals, and lakes, and locally at least does not enter 

 salt or brackish water. 



In addition to the Thailand localities cited in the synonymy, the 

 fish has been collected in various small streams in Nakon Sritamarat; 

 in the Tapi River near Bandon; in the Meklong at Potaram, in the 

 Menam Chao Phya as far north as Lopburi; and in the Sikuk and the 

 Chao Chet, tributaries of the Menam Chao Phya. In addition to the 

 record for Eastern Siam in the Mekong at Kemarat (Fowler, 1937), 

 there is at hand a specimen collected in February 1929 in the Pong 

 Kiver at Pong, in the Mekong drainage. 



The maximum length of specimens collected in Thailand is 20 cm. 

 In the East Indies a length of 33.5 cm. has been reported, and Day 

 gives a length of 45 cm. for India. 



The fully adult fish is usually plain colored. In life the back and 

 sides may be brassy green, the underparts whitish ; the dorsal, adipose, 

 and caudal fins bright green, the anal and ventrals pale salmon with a 

 milky white margin, the pectorals dusky. Young fish always show a 

 light longitudinal band, a dark band above separated from the color of 

 the back by a pale band, and a less distinct dark band below, these 

 juvenile markings sometimes being retained in the adult. A round 

 well-defined blackish or dark brown spot, somewhat larger than the 

 eye, on the side just behind the head is seen in some examples ; this spot 

 is indicated in the figure in Weber and de Beaufort (vol. 2, 1913, p. 336) 

 but is not referred to in their description. 



The union of M. nigriceps Cuvier and Valenciennes (1839) with M. 

 cavasius (Hamilton) (1822) seems proper and desirable. Although 

 nigriceps has not been ascribed to Burma or India, cavasius was 

 reported from Thailand by Karoli (1882), and the existence in the 

 British Museum of two specimens labeled cavasius collected in the Me- 

 wang, Central Thailand, by Arthur S. Vernay has prompted an inquiry 

 as to the species represented by the two names. This inquiry has led 

 to the conclusion that no essential differences are disclosed by the de- 

 scriptions and figures of M. nigriceps as published by Bleeker and 

 Weber and de Beaufort and the description and figure of M. cavasius 

 as published by Day. Bleeker (301, vol. 2, p. 58, 1862) stated that his 

 species macronema (antedated by 7 years by nigriceps which he placed 

 in the synonymy) is very close to cavasius. The supposed differences 

 that he indicated {cavasius having its hood almost smooth, its body 

 more slender, its scapular base smooth, its dorsal higher and more 

 pointed, and its dorsal spine shorter), do not stand the test of analysis 

 and comparison of specimens. 



A critical examination of specimens of the same size in the U. S. 

 National Museum, some called M. cavasius from the Irrawaddy at Man- 

 dalay, Burma, and some called M. nigriceps from the Tale Noi in Pen- 



