PROCEEDINGS OF THE NATIONAL MUSEUM vol. ii9 



Key to Genera and Species of Subtribe Nannostomina 



Second infraorbital bone without bony canal passing in its substance. 



Genus Nannostomus. 2 



Second infraorbital bone with well-developed bony infraorbital canal passing 

 in its substance Genus Poecilobrycon. 7 



Very indistinct primary horizontal stripe present. Secondary or tertiary 

 horizontal stripes absent. Five dark permanent blotches along sides (in 

 life these blotches not fading during exposure of fish to daylight). 



Nannostomus espei (p. 9) 



Primary horizontal stripe present, very well developed. Some species with 

 secondary and tertiary horizontal stripes present. One or two pale oblique 

 bands on sides (in life these bands ordinarily present only when fish kept 

 in dark). Permanent blotches absent 3 



Primary horizontal stripe present, secondary stripe present or absent, tertiary 

 horizontal stripe absent. Teeth in single row on premaxillary, 5 to d 

 (usually 6). Anal fin rays of males slightly to greatly modified, fiatteneG 

 in sagittal plane 4 



Primary, secondary, and tertiary horizontal stripes well developed. Teeth 

 in one row on premaxillary, 7 to 8 (usually 8). Anal fin rays of males 

 completely unmodified in appearance 6 



Perforated scales in lateral line 2 to 4. Adipose fin absent. Anal fin rays 

 iii,9. Anal fin rays of males relatively little modified, not greatly flattened 

 and expanded in sagittal plane 5 



No perforated lateral line scales. Adipose fin present. Anal fin rays iii,8- 

 Anal fin rays of males greatly modified, flattened, and expanded in sagittal 

 plane Nannostomus digrammus (p. 22) 



Secondary horizontal stripe absent. Gill rakers 9 to 10+17 to 18. 



Nannostomus bifasciatus (p. 19) 



Secondary horizontal stripe present. Gill rakers 8+14. 



Nannostomus beckfordi (p. 12) 



Scales 26 to 27 in lateral series. Total vertebrae (including those of Weberian 

 apparatus) 35 to 36. Adipose fin present, either well developed or rudi- 

 mentary. About 11 teeth in second tooth row of dentary. Snout in eye 

 1.0. Least depth of caudal peduncle in standard length 10.0 to 10.4. 



Nannostomus trifasciatus (p. 29) 



Scales 21 to 23 in lateral series. Total vertebrae 31 to 33. Adipose fin 

 absent. Teeth in the second row of dentary 6 to 7. Snout in eye 1.3 to 

 1.4. Least depth of caudal peduncle in standard length 7.8 to 8.5. 



Nannostomus marginatus (p. 32) 



Principal caudal fin rays 10/9, their distribution in lower and upper caudal 

 lobes normal, 10 ending in upper lobe, 9 ending in lower lobe. Total 

 vertebrae 38 to 39. Length of caudal peduncle in standard length 5.3 

 to 6.1 . . . (Subgenus Poecilobrycon) . Poecilobrycon harrisoni (p. 38) 



Principal caudal fin rays 10/9, but 8 rays end in upper lobe and 11 in lower 

 lobe of caudal fin. Total vertebrae 33 to 34. Length of caudal peduncle 

 in standard length 6.0 to 7.5 (Subgenus Nannohrycon). 8 



Scales 28 to 30 in lateral series. Perforated scales in lateral line 2 to 5. 

 Adipose fin present. Gill rakers 9 + 14. Inner tooth row of dentary 

 absent; teeth in outer dentary tooth row 6 to 7. 



Poecilobrycon unifasciatus (p. 42) 



