522 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



the posterior margin of preoperculum." Koumans' figure, together 

 with the specimens now in hand, shows that the long maxillary reaches 

 no farther backward than the anterior margin of the preopercle. 



GNATHOGOBIUS, new genus 



Genotype. — Gnathogobius aXiceae^ new species. 



Moderately elongate ; body compressed ; head broad, depressed, flat ; 

 interorbital space wide; mouth large, maxillary produced backward 

 nearly or quite to opercle; tongue truncate; in upper jaw an outer row 

 of small teeth and a row of very fine teeth behind, in lower jaw a pluri- 

 serial patch of small teeth anteriorly, with some of the lateral teeth 

 enlarged but none canine or caninoid ; gill openings restricted to sides, 

 isthmus broad; body covered with weakly ctenoid scales becoming 

 cycloid anteriorly; region in front of dorsal fin fully scaled to eyes; 

 opercle, base of pectoral fin, and breast scaled; conspicuous lines of 

 papillae on cheek and opercles; dorsal rays VI-I, 7; anal rays I, 7; 

 caudal fin short, rounded ; pectoral fin without free rays. 



This genus represents one of a group of Oriental gobies of the family 

 Gobiidae characterized by a marked development of the jaws, with the 

 maxillary extending on the preopercle or even to the opercle. Other 

 genera in the group are Waitea (Jordan and Scale, 1906), Eugnatho- 

 golius (H. M. Smith, 1931), Mahidolia (H. M. Smith, 1932), and 

 Pseudogohiopsis (Koumans, 1935). The relations of these genera to 

 one another are shown in the following synopsis, in which Waitea. a 

 non-Thailand genus, is included because it has become involved with 

 Mahidolia: 



la. First dorsal fin with 5 spines ; branched dorsal rays 7, branched anal rays 6 ; 

 caudal fin rounded, shorter than head ; head depressed ; interorbital space 

 2 times eye; eyes very small; gill openings restricted; isthmus broad; 



head scaleless Eugnathogobius 



16. First dorsal fin with 6 spines ; eyes of moderate size. 



2a. Scales on top of head extending to eyes ; scales on opercle ; head depressed. 



3a. Most anterior scale on top of head large, median, unpaired ; gill openings 



wide, continued well forward ; isthmus narrow ; interorbital space 



narrow, less than eye ; branched dorsal rays 6 or 7, branched anal rays 



6 ; caudal fin short, bluntly pointed Pseudogobiopsis 



3&. No median unpaired scale on top of head; gill openings restricted, not 

 continued well forward ; isthmus broad ; interorbital space twice as 

 wide as eye; branched dorsal rays 8, branched anal rays 8; caudal 



fin short, rounded Gnathogobius 



2&. A few small scales in front of dorsal fin, but none extending to eyes; no 

 scales on opercle ; head compressed ; gill openings wide, extending well 

 forward ; isthmus narrow ; interorbital space less than half eye ; branched 

 dorsal rays 10, branched anal rays 9 ; caudal fin short, rounded. 



Mahidolia 



2c. No scales on top of head or on opercle; head compressed; gill openings 



restricted ; isthmus broad ; interorbital space less than half eye ; 



branched dorsal rays 10, branched anal rays 12; caudal fin long, 



lanceolate "Waitea 



