GOBIES. 487 



having very small teeth and feeble jaws. In April the males 

 lose the small teeth, which are replaced by very long and 

 strong teeth, the jaws themselves becoming stronger. The 

 teeth of the females remain unchanged. In July and August 

 all the adults die off, and in September only the fry are to 

 be found. 



There are several other genera, closely allied to Gobius, 

 as Euctenogobvus, Lophiogohius, DoliicMliys, Apocryptes, Evor- 

 thodtis, Gohiosoma and Goliodon (with scaleless body) Triccno- 

 pliorichthys. 



SiCYDiUM. — Body covered with ctenoid scales of rather small 

 size. Cleft of the mouth nearly horizontal, with the upper jaw 

 prominent ; lips very thick ; the lower lip generally with a series 

 of minute horny teeth. A series of numerous small teeth in 

 upper jaw, implanted in the gum, and generally movable ; the 

 lower jaw with a series of conical widely-set teeth. Two dorsal 

 fins, the anterior with six flexible spines. Ventral fins united, 

 and forming a short disk, more or less adherent to the abdomen. 



Small freshwater fishes inhabiting the rivers and rivulets 

 of the islands of the tropical Indo-I'acific. About twelve 

 species are known ; one occurs in the West Indies. Lentipes 

 from the Sandwich Islands is allied to Sicydium. 



Periophthalmus. — Body covered with ctenoid scales of small 

 or moderate size. Cleft of the mouth nearly horizontal, with the 

 upper jaw somewhat longer. Eyes very close together, imme- 

 diately below the upper profile, prominent, but retractile, with a 

 well-developed outer eyelid. Teeth conical, vertical in both 

 jaws. Two dorsal fins, the anterior with flexible spines ; caudal 

 fin with the lower margin oblique ; base of the pectoral fin free, 

 with strong muscles. Ventral fins more or less coalesced. Gill- 

 openings narrow. 



The fishes of this genus, and the closely-allied BoleopMlial- 

 imis, are exceedingly common on the coasts of the tropical 

 Indo-Pacific, especially on parts covered with mud or fucus. 

 During ebb they leave the water and hunt for small crusta- 



