FRESH-WATER FISHES OF SIAM, OR THAILAND 475 



The local phallostethids may be recognized readily by the backward 

 position of the 6- to 8-rayed soft dorsal fin, which is preceded by a 

 highly reduced spinous dorsal fin consisting of a single short spine or 

 two short spines ; by the absence of ventral fins ; and by the presence 

 in the male of a complicated fleshy appendage (priapium) suspended 

 from the head and shoulder girdle, supported by a complex skeleton, 

 having anal, urinary, and genital openings, and bearing certain long, 

 free, slender, curved bony structures presumably used as claspers ; one 

 of these bony processes (toxactinium) may project from the anterior 

 part of the priapium, and one or two (ctenactinia) may project from 

 the posterior part. In the female the ventral opening is between the 

 pectoral fins. 



In 1935 Myers proposed a new suborder (Phallostethoidea) for 

 these fishes, and in 1940 Berg gave them full ordinal rank under the 

 name Phallostethiformes, recognized the families Phallostethidae and 

 Neostethidae separable on the presence or absence of the toxactinium, 

 and placed them immediately after the Cyprinodontes, to which he con- 

 sidered them related, but as manifesting a step toward the Percif ormes. 



The two genera of Phallostethidae known from Thailand may be 

 differentiated as follows : 



la. Toxactinium present, its base covered by a shieldlike mass (pulvinulus) ; 

 posterior end of priapium without soft comblike projections ; first dorsal 

 fin with a single spine Phenacostethus 



lb. Toxactinium absent ; pulvinulus not shieldlike ; posterior end of priapium 

 with soft comblike projections ; first dorsal fin with two spines in local 

 species (one spine in outside species) Neostethus 



Genus PHENACOSTETHUS Myers 



Phenacostethus Mtees, Amer. Mus. Novit., No. 295, p. 6, 1928. (Type, Phena- 

 costethus smithi Myers.) 



PHENACOSTETHUS SMITHI Myers 



Phenacostethus smithi Myeks, 1928, p. 6, figs. 1, 2 (Bangkok).— Smith, 1929, 

 p. 13 (Bangkok).— Myers, 1937, p. 138 (Bangkok).— te Winkel, 1939, pp. 

 59-69, figs. 1-5 (detailed account of internal anatomy). 



Phenacostethus thai Fowiek, 1937, p. 219, figs. 189, 190 (Bangkok). 



When the writer first went to Thailand in 1923, he was attracted 

 by certain small, transparent fishes that inhabited fresh waters within 

 the city of Bangkok, and he saw at once that they were representa- 

 tives of the extraordinary family that had been brought to light by 

 Regan in 1913 and 1916. They were similar to the species described 

 from the Malay Peninsula as Neostethus lankesteri Eegan, and the 

 writer assumed they represented that form and published (1927e) a 

 note about them under that name. The next j-ear (1928) Dr. George 

 S. Myers, having examined 19 specimens collected by the present 



