298 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. X. 



common in the upper courses of rocky streams in the Rio Chagres Basin. 

 From B. argenteus of the Pacific slope, its nearest relative, it differs 

 mainly in the smaller scales. 



Habitat: Atlantic slope of Panama. 



43. Brycon argenteus Meek & Hildebrand. 



Brycon argenteus Meek & Hildebrand, Field Mus. Nat. Hist. Pub., 



Zool. Ser., X, 1913, 84 (Rio Aruza, Darien). 



Head 3.5 to 4.45; depth 2.96 to 3.84; D. u, rarely 10; A. 24 to 28; 

 scales in lateral series 43 to 48. 



Body elongate, compressed, profile straight over eyes, somewhat 

 elevated at nape; head small; snout pointed, 3.46 to 4.2 in head; eye 

 2.86 to 4.25; interorbital 2.4 to 3.5; mouth moderate; upper jaw a little 

 in advance of the lower; maxillary reaching to or slightly past anterior 

 margin of pupil, 2.1 to 2.44 in head; premaxillary teeth laterally in only 

 2 series, the second series well covered by the lower lip; the last or trans- 

 verse series situated close in front of the teeth in lower jaw, touching 

 them when mouth is closed; the outer series of premaxillary teeth 14 in 

 number; first series in lower jaw with 8 strong teeth of about equal size 

 and 2 or 3 smaller ones behind laterally; gill-rakers rather small, 12 to 

 14 on lower limb of first arch; lateral line decurved, below median line 

 of side; scales large, regularly placed, 12 to 14 vertical series crossing 

 back between dorsal and adipose; 2 longitudinal rows between lateral 

 line and base of pectoral; dorsal fin inserted a little nearer base of caudal 

 than tip of snout; adipose fin only half as far from base of upper caudal 

 ray as base of last dorsal ray; caudal fin forked, the lower lobe the 

 larger; anal fin short, its base about as long as head, its origin below or 

 slightly behind base of last dorsal ray, a little nearer base of caudal than 

 base of pectorals; ventral fins usually not quite reaching vent, inserted 

 a little nearer origin of anal than base of pectorals; pectoral fins inserted 

 under margin of opercle, sometimes reaching base of ventrals, but often 

 failing to reach them by 2 or 3 rows of scales. 



Color silvery, bluish above, pale silvery below; sides plain in large 

 specimens, the smaller ones often with indistinct dark reticulations; 

 very young with a dark lateral band. A large black caudal spot present : 

 no opercular spot; a blackish spot or bar at shoulder, this indistinct in 

 some of the larger specimens. 



The present collection contains 340 specimens, ranging in length 

 from 30 to 230 mm. This species was taken in the Rio Chorrera and 

 in the Rio Bayano and Rio Tuyra basins. It is common in the upper 

 courses of rocky streams, reaching a smaller size than B. striatulus 

 and of less value as food. 



