FRESH-WATER FISHES OF SIAM, OR THAILAND 



111 



fin longer than head, deeply forked, longest rays 2.5 times the median 

 rays; anal rays iii, 5, longest less than 0,7 of longest dorsal ray; 

 ventral rays i, 7, longest about 1.2 in longest dorsal ray, origin of fin 

 under eleventh scale of lateral line and midway between tip of snout 

 and base of caudal fin ; pectoral somewhat longer than head, 1.4 times 

 length of ventral, rays i, 14. 



Coloration: A silvery longitudinal band from head to caudal fin 

 overlain posteriorly by a dark stripe which begins as a narrow stripe 

 opposite the dorsal fin and exf)ands on the caudal peduncle; caudal fin 

 bright yellow, with a sharply defined black margin widest on the lobes ; 

 other fins hyaline. 



Figure 12. — Rat bora retrodorsalis, new species: Type (U.S.N.M. No. 119520). Drawn by 



Mrs. Alice C. Mullen. 



Type and paraty pes. —The type (U. S. N.M. No. 110520), 14.8 cm. 

 long, was taken March 18, 1924, from a pond in Bangkok conn£cted 

 with a canal and thence with the Menam Chao Phya. Paratypes are 

 U.S.N.M. Nos. 103279, 108119, 108120, and 118444. 



Remarks. — This form has been found to be common and widely 

 distributed in Central and Peninsular Thailand. Other specimens are 

 at hand from Bung Borapet, the Menam Chao Phya, and the Menam 

 Tadi near Bandon. 



The maximum length of available specimens is 15 cm. 



When this fish swims at or near the surface in the turbid waters of 

 ponds, canals, and streams, it would often be practically invisible 

 except for the sharply marked black edge on the caudal fin. 



This species is similar to R. argyrotaenia but differs therefrom in a 

 number of features. The most noticeable difference is in the position 

 of the dorsal fin which, in R. argyrotaenia, arises midway between the 

 tip of the snout and the posterior row of scales on the caudal peduncle, 

 opposite the eleventh scale of the lateral line (Weber and de Beaufort) . 

 In the present form the origin of the dorsal fin in the type is midway 



