FRESH-WATER FISHES OF SIAM, OR THAILAND 513 



36. First dorsal fin with 6 spines; teetli pluriserial in both jaws (uniserial 

 in one jaw in Oxyurichtliys) ; head naked or partly scaled; body fully 

 scaled. 

 6a. Maxillary greatly produced backward, extending to, or nearly to, 

 or onto the preopercle. 



la. Lower jaw and snout with short barbels Pogonogobius 



76. Lower jaw and snout without barbels ; head depressed or com- 

 pressed. 

 So. Head depressed, scaled on opercle and to eyes ; tongue truncate 

 or emarginate. 

 9a. Branched dorsal and anal rays 6 or 7; caudal fin short, 

 bluntly pointed ; most anterior scale on top of head large, 

 median, unpaired ; gill openings wide, isthmus narrow ; 

 interorbital space narrow, less than eye__ Pseudogobiopsis 

 96. Branched dorsal and anal rays 8; caudal fin short, rounded; 

 no anterior median unpaired scale on top of head ; gill 

 openings restricted, isthmus narrow, interorbital space 



wide, twice eye Gnathogobius 



86. Head strongly compressed, unsealed on top and on opercles ; 

 branched dorsal and anal rays 9 or 10 ; tongue rounded. 



Mahidolia 



66. Maxillary not greatly produced backward, extending to, under, or 



slightly behind eye. 



lOfT. Teeth in upper jaw in one row, strong, caninoid ; teeth in lower 



jaw in 2 to 4 rows, inner row may be enlarged ; branched dorsal 



and anal rays 10 to 13 ; caudal fin long and pointed. 



Oxyurichthys 

 106. Teeth in both jaws pluriserial. 



11a. Upper pectoral rays free and silky ; head depressed ; top of 

 head scaled backward from eyes; tongue bilobed. 



Bathygobius 



116. Upper pectoral rays not free and silky (except in some species 



of Acentrogohius) . 



12a. Scales ctenoid posteriorly, often becoming cycloid anteriorly, 



24 to 50 in longitudinal series. 



13c. Top, sides, and under parts of head with conspicuous 



ridges and flaps of skin ; 48 to 50 scales in longitudinal 



series; predorsal scales extending over anterior part 



of opercles or nearly to eyes ; opercles and preopercles 



with embedded scales ; tongue rounded Macgregorella 



136. Head without ridges and flaps of skin. 

 14a. Scales on opercle, if any, cycloid. 



15a. Scales on top of head extending to or between eyes. 

 16a. Foremost scale in median line on top of head large 

 and unpaired; head compressed; opercles scaled 

 or not ; outer row of teeth in each jaw enlarged ; 

 outer row in lower jaw extending only half length 

 of jaw, last teeth not strongly developed ; a pair 

 of postsymphyseal canines and some canines in 

 inner row of lower jaw may be present ; tongue 

 rounded Stigmatogobius 



