238 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



KEY TO THE GENERA 



a. Preopercle without serrations, the margin being entire; second dorsal and 



second anal spines not greatly enlarged . Gerres (p. 238) 



aa. Preopercle distinctly serrate; second dorsal and second anal spines notably 

 enlarged Diapterus (p. 240) 



Genus GERRES Cuvier, 1924 



Body moderately elongate, compressed; preorbital and preopercle 

 entire; second dorsal and second anal spines not greatly enlarged; 

 second interhaemal spine long, spear-shaped. 



A single widely distributed species ranges into Peru. 



GERRES CINEREUS (Walbaum) 



Chavela 



Mugil cinereus Walbaum, 1792, p. 228, Bahamas (description based on Catesby 



pre-Linnaean) . 

 Xystaema cinereus Jordan and Evermann, 1898, p. 1372, fig. 556 (description; 



range; synonymy). 

 Xystaema simillimum Evebmann and Radcliffe, 1917, p. 91, Rfo de Eten, Eten, 



Peru (synonymy; description). 

 Gerres cinerexis Meek and Hildebrand, 1925, p. 589, both coasts of Panama 



(synonymy; description; range). 



Head 2.9 to 3.1; depth 2.2 to 2.6; D. IX, 10; A. Ill, 7; P. 15; scales 

 41 to 44. 



Body rather strongly compressed, its greatest thickness scarcely a 

 third its depth; back elevated; profile from snout to nape nearly 

 straight; outline under snout and anterior part of eye dropping rather 

 abruptly, slightly concave; head rather small, compressed; caudal 

 peduncle fairly slender, 2.7 to 2.8 in head; snout abruptly pointed, 3.5 

 to 4.0; eye 2.7 to 3.1; interorbital 3.5 to 3.8; mouth small, nearly 

 horizontal, terminal; maxillary reaching slightly beyond anterior 

 margin of eye, 2.8 to 3.1 in head; teeth in jaws small, pointed, in a 

 narrow band in each jaw; premaxillary groove broad, not restricted 

 anteriorly, free from scales ; gill rakers small, shorter at angle than 

 anteriorly on lower limb of first arch, 7 or 8 more or less developed 

 on lower and 3 or 4 on upper limb of first arch; scales moderate, with 

 thin membranous edges, rows above lateral line parallel with it, 

 5 between it and base of first dorsal spine, and only 4 complete rows 

 below base of first soft ray, extending on base of caudal and ventral, 

 and forming a broad sheath at base of dorsal and anal; dorsal spines 

 fairly slender, the third usually longest, 1.7 to 1.8 in head; caudal 

 deeply forked, the lobes pointed, of about equal length, longer than 

 head; anal spines moderate, the second somewhat stronger than the 

 third, reaching to or not quite to tip of the third, 1.8 to 2.4 in head; 

 ventral reaching to or beyond vent, inserted just behind base of pec- 

 toral, with a slender spine contained 1.8 to 2.1 in head; pectoral long, 



