GEEEES. 37 



Fam. 9. LIOGNATHID^. 



The Liognathidse comprise the four genera Gerres, Pentaprion, Liognathus, and 

 Gazza. The three last-named appear to be exclusively marine and are confined to the 

 tropical Indo-Pacific. Gerres is found in all tropical seas, and most of the species 

 appear to freely enter fresh water. 



1. GERRES, Cuv., 1829. 

 Gerres, Gunth. Cat. Fish. iv. p. 252 (1862). 



Eucinostomus, Ulcema, Xystcema, and Gerres, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 1898, 

 pp. 1367, 1371, 1372, and 1373. 



Body compressed ; scales large or moderate, c3'oloid or finely ctenoid. Lateral line complete. Mouth 

 moderate, very protractile ; maxillary exposed ; jaws equal anteriorly ; bands of small vUliform teeth in 

 jaws ; palate toothless. Prceorbital and prasoperculum entire or finely serrated. A single dorsal with 

 IX 10 rays, with a scaly sheath at the base ; second or third dorsal spine the longest ; anal with II-III 

 7-9 rays; caudal forked; pectoral asymmetrical, pointed ; ventrals a little behind the base of pectorals, 

 with I 5 rays ; a scaly process at base of spine of each ventral fin. 



Ilah. Tropical seas, entering rivers. 



The American species of Gerres number seventeen, and although only a small 

 proportion of these have been recorded from rivers or lakes in Mexico and Central 

 America, we may feel quite sure that most of them are to be met with there. It is 

 rather a difficult matter to know how to deal with such a group in a work on fresh- 

 water fishes, but I have thought it more useful to prepare a synopsis of all the 

 American species, based on an examination of the available material, rather than to 

 give descriptions of the few definitely known to occur in the fresh waters of Mexico 

 and Central America. 



Synopsis of the Species. 

 I. Prseoperculum entire. 

 A. Anal III 7. 



1. Second anal spine \-\ the length of head ; second dorsal spine a little longer than 



third ; depth of body 2^-2^ in the length. 



5 or 5^ scales between lateral line and middle of dorsal fin 1. cinereus. 



4 scales between lateral line and middle of dorsal fin 2. simillimus. 



2. Second anal spine from less than ^ to slightly more than .!.- the length of head ; second 



dorsal spine a little shorter than third. 

 a. Praemaxillary processes (measured from anterior edge of upper jaw to their posterior 

 extremities) more than \ the length of head. 

 Snout a little shorter than eye; maxillary extending to below anterior margin 

 of eye; depth of body 21-2n in the length; 7 gill-rakers on the lower 

 part of anterior arch 3. (lula. 



