382 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



darker spot above the humeral process. The body is rather slender 

 (depth 5.75 in standard length) ; the nasal barbels reach far beyond 

 the eyes, both the maxillary and mandibular barbels extend behind 

 the base of the pectorals, and the mental barbels reach the branchial 

 openings; the dorsal fin is separated from the adipose fin by a space 

 equal to the length of the adipose base, which exceeds the length of the 

 anal fin; the caudal fin, deeply forked with upper lobe the longer, is 

 more than 1.5 times the length of the head; the pectoral spine is 

 longer than the dorsal spine and equal to the distance from the pos- 

 terior nostril to the gill opening; the ventrals, somewhat more than 

 0.5 length of head, extend to a long, slender anal papilla. 





Figure 84. — Leiocassis stenomus (Cuvier and Valenciennes). Drav/n by Nai Chote 

 Suvatti; courtesy of the Thailand Government. 



Genus MYSTUS Scopoli 



Mystus Scopoli, Introductio ad historiam uaturalem, p. 451, 1777. [We have 

 not been able to determine vpith satisfaction the genotype of Mystus Scopoli. 

 The situation is in need of study, and a separate paper would be required 

 to clarify the nomenclature of Mystus and its various uses. — L.P.S.] 



The fishes now placed in the genus Mystus have borne many generic 

 names. The earliest available name is Mystus, first used by Gronow 

 in 1763 and validated by Scopoli in 1777. For many years the fishes 

 were called Macrones (Dumeril, 1856), although that name was pre- 

 occupied in entomology (1841). Aoria, proposed by Jordan (1919, p. 

 341) as a substitute for Macrones, had some usage, although if Mystus 

 were not acceptable the Bleekerian names Hemibagms, Hypselobagrus, 

 and Aspidohagr'us were available. 



The mystid catfishes are numerous as to species and individuals in 

 the fresh waters (rivers, canals, lakes) of Thailand. Most of them 

 are small; one species reaches a length of more than 60 cm. in this 

 country. All are eaten and some of them appear regularly in the mar- 

 kets of Bangkok and other large communities. 



The usual vernacular generic name for these fishes throughout 

 Thailand is pla kayeng, meaning ugly or repulsive fish. Various 

 qualifying names are used for the different species. The word kayeng 

 is often shortened to yetig. 



