370 MEMOIRS OF THE CARNEGIE MUSEUM 



Twenty-one specimens, 102-149 mm. Tumatumari. (C. M. Cat. No. 

 1815a-e; I. U. Cat. No. 12105.) 



Head 4-4.2; depth 3.25-3.33; D. 11; A. 21-23; scales 8.5-41 to 44-3.5. Eye 

 3.4-3.75 (3 in the smallest). 



Compressed, ventral profile more strongly arched than the dorsal; head 

 pointed; area between ventrals narrowly rounded. 



Fontanels becoming closed when specimens reach a size of about 75 mm. 

 Second suborbital covering the entire cheek in the adult; maxillary with teeth along 

 its entire margin, slipping under, but not concealed by the preorbital; snout pro- 

 jecting; premaxillary with eight to ten teeth in the outer row; four large teeth in 

 the outer row of each side of the lower jaw, and smaller teeth on the sides. 



Origin of dorsal about equidistant from base of middle caudal rays and anterior 

 margin of the eye; margin of dorsal rounded; adipose fin large; caudal forked, the 

 lobes not twice as long as the middle rays, the middle rays not prolonged. 



Anal slightly emarginate; ventrals not reaching anal; pectorals barely reaching 

 ventrals. 



Iridescent blue with faint dark cross-lines ; a dusky humeral spot; adipose and 

 margin of caudal dusky or black, the caudal sometimes watered. Dorsal, ventrals, 

 middle of anal lobe, and a band on each caudal lobe, rusty. 



Subfamily Bryconin^e. 



Brycon Mtiller and Troschel. 



Brycon Muller and Troschel, Hora3 Ichth., I, 1845, 15 {falcatus). 

 Chalcinopsis Kner, SB. Akad. Wiss. Mt'mchen, 1863, 226 (striatulus) . 

 Megalobrycon Gunther, Proc. Zool. Soc. London, 1869, 423, fig. 1 (cephalus). 

 Bryconodon Eigenmann, Smiths. Misc. Coll., Quarterly Issue, XLV, 1904, 146 



(orthotcenia) . 

 Triurobrycon Eigenmann, Ann. Carnegie Mus., VI, 1909, 33 (lundii). 



Type, Brycon falcatus Muller and Troschel. 



With the characters of Holobrycon, but the skull with two large fontanels. 



Two species of this genus have been recorded from British Guiana. They 

 may be distinguished as follows: 



Key to the Guiana Species of Brycon. 

 a. Middle caudal rays prolonged, forming a projecting point; base of anal and a large V-shaped caudal spot 



black; dark lines along the rows of scales falcatus. 



aa. Middle caudal rays prolonged, the caudal emarginate; fins largely black; dark lines between the rows of 

 scales siebenthalae. 



