298 Fretp Museum or Natura History — Zoétoecy, Vor. 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. 11, 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. 
