528 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



With the exception of A. nebulosus^ of which too few specimens 

 are avaihible for comparison with other species, the Thai representa- 

 tives of the genus Acentrogobius are distinguishable by the following 

 characters : 



la. About 30 or fewer scales in longitudinal series. 

 2a. Upper pectoral rays free and silklike ; no scales on opercle or preopercle ; 

 scales in longitudinal series 2G to 28, in transverse series 9, in predorsal 

 region 10 to 12 ; body and head green to yellow, with 6 to 8 longitudinal 

 lines of dark brown or black spots, several of the lower rows of larger, 

 elongate spots ; all fins except ventrals with rows of dark spots ; ventrals 



brown or black ornatus 



2b. Upper pectoral rays not free and silklike. 

 3a. Opercle and preopercle scaleless. 



4a. Predorsal scales about 21 ; scales in longitudinal series about 28, in 

 transverse series 9, body and head light brown ; 4 diffuse dark 

 brown spots along middle of side alternating with 4 similar spots on 

 back; a large round black spot at upper end of gill opening; first 

 dorsal fin rich brown, most intense on either side of fifth and sixth 

 rays, and dorsal fin elaborately decorated with brown and plumbeous 

 in transverse lines, with a narrow brown border, a series of elongate 

 plumbeous spots edged above and below with a narrow colorless 

 stripe, a broad median band of brown and plumbeous, and a basal 

 band of plumbeous spots separated from the median band by a clear 

 line ; caudal rays brown, membranes mostly clear ; anal fin dusky ; 

 ventral fins with central part plumbeous ; pectorals pale brown. 



simulans 



46. Predorsal scales about 9 to 14 ; scales in longitudinal series about 30, in 



transverse series 8 or 9. 



5a. Any or all of first 3 dorsal spines in male produced into a long 



slender filament. 



6a. General color green, each scale of back and sides with a round spot 



of pearly blue ; a blue-black spot at upper angle of gill opening ; 



first dorsal fin green to yellowish, with a basal row of pale 



yeUow spots; second dorsal, caudal, and anal fins dark violet 



to black, with transverse rows of white spots and with a very 



narrow edge of red or orange ; ventrals black, with red tips ; 



pectorals black, with narrow light margin and broad green base. 



cyanomos 



6&. General color dusky, with obscure darker blotches; dorsal, anal, 



and ventral fins dusky purple; caudal and pectoral fins deep 



orange or orange-red, the pectorals purplish at base, the caudal 



with small black spots on membranes forming 6 to 8 transverse 



bands oligactis 



5&. None of rays of first dorsal fin produced into a long slender filament. 

 7a. A brown spot at upper base of caudal fin ; body green, with snowy 

 spots ; each scale of side with a round brown spot. 



chlorostigmatoldes 



76. Five brown blotches or doubled spots along midaxis of body, the 



last at midbase of caudal fin ; smaller and fainter brownish 



spots on body reichei 



