38 PROCEEDINGS OF THE NATIONAL MUSEUM vol. ii9 



in eye diameter. The members of this genus have, correlated with the 

 long snout, a longer, narrower ethmoid and prevomer, a longer ant- 

 orbital and infraorbital, and a longer mesopterygoid and nasal bone 

 than do members of the genus Nannostomus. Primary and secondary 

 horizontal stripes are present in all species, but a tertiary horizontal 

 stripe is absent in 2 species. The anal fin rays may or may not be 

 modified in males. The body is elongate in all species, the depth 

 being 4.5 to 5.7 in standard length. 



The name Poecilobrycon is derived from the generic names PoecUia 

 and Brycon, the implied meaning being a Poecilia-\ike Brycon, i.e., a 

 Brycon-like fish or characid with characters of the poeciliid fishes. 

 This name probably occurred to Eigenmann because of the small mouth 

 and numerous tooth cusps in Poecilobrycon. However, in detail, the 

 mouth of nannostominans bears little resemblance to that of any 

 poeciliid fish. 



Subgenus Poecilobrycon Eigenmann 



Diagnosis. — As in all members of Nannostomus, 10 principal rays 

 of upper 4 hypural bones all enter upper caudal lobe. Lower lobe of 

 caudal fin with dark pigment only at its base. Normal resting and 

 swimming position horizontal. See under the subgenus Nanno- 

 hrycon for a discussion of this character. 



Poecilobrycon harrisoni Eigenmann 



Figures 9, 10 



Poecilobrycon harrisoni Eigenmann, 1909, p. 43 (original description; type locality: 

 British Guiana, Canal at Christianburg, Demerara River; holotypein Chicago 

 Natural History Museum) ; 1910, p. 427 (listed) ; 1912, p. 284, pi. 37, fig. 1 

 (description; British Guiana).— Hoedeman, 1950, p. 22 (copied descrip- 

 tion); 1954b, p. 89 (description; British Guiana). — Weitzman, 1964, p. 136 

 (osteology and relationsliips) . 

 Archicheir viinutus Eigenmann, 1909, p. 46 (original description; type locality: 

 British Guiana, Canal at Christianburg, Demerara River; holotype in Chicago 

 Natural History Museum) ; 1910, p. 427 (listed) ; 1912, p. 287, pi. 37, fig. 5 

 (description; British Guiana). 

 1 Nannostomus kumuni Ladiges, 1948, p. 30 (name only listed, nomen nudum). 

 1 Nannostomus cumuni Arnold, 1950, p. 63 (original description, from life, no type 

 specimens) . 

 Diagnosis. — This species may be distinguished from all other 

 nannostominans by its greater number of vertebrae, 38 to 39, con- 

 trasted to 31 to 36. It may be recognized further by the following 

 combination of characters: Second tooth row of dentary with 12 to 

 15 teeth; 7 + 13 gill rakers; iii,9 anal fin rays; 27 to 30 scales in lateral 

 series; maxillary tooth present; fairly long caudal peduncle, 5.3-6.1 

 in standard length. 



