FRESH-WATER FISHES OF SIAM, OR THAILAND 515 



21&. Opercle and preopercle sometimes with a few 

 large scales on upper part ; scales in longitu- 

 dinal series 25 to 40 ; outer and inner rows of 

 teeth in each jaw enlarged, unequal, wide-set, 

 outer row curved ; gill openings wide ; chin 



prominent ; tongue bilobed Glossogobius 



17c. Head globose ; upper part of ojjercle, preopercle, 

 and cheek with patches of small scales ; scales in 

 longitudinal series 29 to 40 ; teeth in 4 to 6 rows 

 in front of each jaw, reduced to 2 or 3 rows at 

 sides ; outer row more or less enlarged ; a pair 

 of recurved canines laterally on lower jaw ; 

 tongue truncate ; mouth small, maxillary usu- 

 ally not reaching vertical from anterior margin 



of eye Creisson 



156. Scales on top of head not extending to eyes. 



22o. Predorsal scales not extending beyond opercle ; oper- 

 cle and preopercle naked; scales in longitudinal 

 series 38 to 42 ; teeth in upper jaw with outer row 

 enlarged, in lower jaw with inner row enlarged, 

 some teeth at symphysis of lower jaw and poste- 

 riorly may be canine or caninoid ; tongue truncate 

 or slightly emarginate ; caudal fin bluntly or acute- 

 ly pointed Oligolepis 



22&. Head nearly or entirely naked ; sometimes a post- 

 orbital row of scales extending above opercle; 

 scales in longitudinal series 25 to 45 ; teeth in outer 

 row of each jaw enlarged, in outer row of lower 

 jaw extending only half length of jaw, the last 

 teeth caniniform ; tongue broadly rounded, trun- 

 cate, emarginate, or mucronate Ctenogobius 



146. Scales on opercle ctenoid, head otherwise naked; pre- 

 dorsal region naked, with a median groove ; scales in 

 longitudinal series about 25 ; outer row of teeth in each 

 jaw enlarged, no canines ; tongue truncate ; gill open- 

 ings restricted, isthmus broad Brachygobius 



126. Scales cycloid, 75 to 140 in longitudinal series; head com- 

 pressed ; opercles and cheeks naked ; tongue truncate ; max- 

 illary extending beyond eye; caudal fin obtusely to 

 acutely pointed and longer than head ; gill openings very 

 wide Cryptocentrus 



Genus GOBIODON Bleeker 



Gobiodon Bleekek (151), Nat. Tijdschr. Nederl. Indie, vol. 11, p. 407, 1856. 

 (Type, Goiiodon heterospilos Bleeker.) 



The gobies of this genus are widely distributed in the Pacific and 

 Indian Oceans and easily recognizable by their small size ; oyate, com- 

 pressed, scaleless body; large, deep head; small, oblique mouth; plu- 

 riserial teeth, with postsymphyseal canines in lower jaw; dorsal fins 

 contiguous or partly united ; short rounded caudal, and pectorals, and 

 very small, cup-shaped ventrals. The color variations have given rise 



