1903.] NATURAL SCIENCES OF PHILADELPHIA. 523 



Caudal moderate, the depth of the cleft about f the length of the 

 lobes. 



Anal moderately long, its first 5 rays high, equal to distance from 

 tip of snout to posterior margin of preopercle; the last half of the anal 

 but ^ as high. 



Pectorals small, reaching f distance to ventrals. 



Ventrals small, reaching f distance to origin of anal. 



In formalin the specimens are almost without color. In some the 

 middle caudal rays are dusky, and a grayish band, probably silvery 

 in life, extends from the base of the caudal to the hmiieral region. 

 The fins are immaculate. 



Scales 5^-37-4^; A. 19-26; D. 9; depth 3^; head 4; eye 3. The 

 following table gives the measurements of eight specimens: 



Min. Max. Average. 



Lengthinmm 37.0 46.0 40.5 



Depth 3.5 3.75 



Head 4.0 4.0 



Eye 2.5 3.0 



Teeth in maxillary 2 2 



Anal 10.0 26.0 



Scales 4.5 to 5.5-35 to 38-4 to 4.5. 



73. Tetragonopterus orbicularis Cuv. and Val. 



Four specimens (252), Arroyo Trementina. It is possible that these 

 specimens are the young of chalceus. Depth 2 in the length ; Lat. 1., 35. 



74. Tetragonopterus chalceus Agassiz. Mojarra. 



Tetragonopterus rufipes Yal. in D.Orb. Voy. Amer. Merid. Poiss, PI. 11, fig. 1. 



Four specimens, Asuncion (86, 13) ; Arroyo Trementina (256). Anal 

 34-37; lat. 1., 30 or 31. 



The description of rufipes makes it a distinct species, but the figure 

 shows it to have an anal much shorter than that described . 



75. Brycon hilarlii (Cuv. and VaL). 



Chalceus hilarii Cuv. and Val., XXII, 246, 1848; Castelnau Anim. Amer. 

 . Sud. Poiss., 68, PL 36, fig. 1, 1855: Ivner, Denksch. Acad. Wien, 1860, 



XVITI, 10. 

 Brycon hilarii Gunther, Cat. Fish Brit. Mus., V. 336, 1864. 

 Chalceus orbigmjanus Cuv. and Val., XXII, 249, Kner, I. c, 11. (Rio de la 



Plata, Rio Guapore.) 



One specimen (194), 21 cm., Arroyo Trementina. 



Head 4i; depth 3{; D. 11; A. 27; V. 8; P. 14; scales 15-75-12. 



A robust species. Body moderately deep, depth 3^. Upper pro- 

 file of head nearly straight to base of occipital process, where the profile 

 rises slightly more rapidly for about ^ way to the origin of the dorsal ; 

 the other f almost straight and rising to the origin of the dorsal at a 



