62 THE AMERICAN CHARACIDAE. 



Fresh specimens from the Essequibo River have the fins more or less suf- 

 fused with red. The first prolonged anal ray milk-white, the first fully formed 

 dorsal ray either dark or milk-white. In these specimens there is a humeral 

 spot prolonged above and below with a bar and a second bar fainter but evident 

 extends down from the dorsal parallel with the first. There is a well-marked 

 dark band-like spot at the base of the caudal. These approach T. argenteus 

 in color. The first three developed rays of the dorsal sometimes reach the 

 caudal, the first three anal rays are also sometimes prolonged to a length about 

 two thirds that of the anal base. 



No humeral bars in old alcoholic specimens in which the caudal spot is 

 more or less obscure with age; dorsal membranes thickly peppered; general 

 color bright and iridescent, silvery. 



Air-bladder very large, the sections conical, the posterior about twice as 

 long as the anterior, sharply pointed behind, its largest diameter, at its base, 

 equals about half the length of the head. 



Alimentary canal somewhat longer than the entire fish. 



Vertebrae 10 + 19; occipital process extending much beyond the posterior 

 face of the skull. 



3. Tetragonopterus huberi Steindachner. 



Tetragonopterus huberi Steindachner, Anz. K. akad. wiss. Wien, 1909, no. 12, p. 172 (Rio Pums); 

 Eigenmann, Rept. Princeton univ. exped. Patagonia, 1910, 3, p. 438. 



Habitat. — Rio Purus, Upper Amazon Basin. 



This species known only from the brief description of two specimens is said 

 to differ from T. argenteus chiefly in having its caudal completely scaled. It is 

 evidently closely allied if not identical with T. chalceus. 



Head 2.7; depth 1.66; D. 11; A. 32; scales 8.5-31-4.5. Eye 2.7 in the 

 head; interorbital 2.33. 



Belly with lateral keels; profile of head concave, that of nape very convex; 

 maxillary with 3-4 teeth; height of prolonged dorsal rays 3 in the length; pec- 

 torals little shorter than head, reaching beyond origin of ventrals; ventrals 

 H in the head; origin of ventrals in front of the vertical from the dorsal; pre- 

 dorsal area keeled; distance between dorsal and adipose equal to the head. 



A row of scales along the base of the anal; traces of two dark vertical 

 humeral bands; caudal spot wanting in a small specimen, faint in a large one. 



