236 Annals of the Carnegie MusEu^r. 



I have been unable to assign a place to Salmo undiilatus and Serra- 

 salmo scotopterus of Schomburgk, Fishes of British Guiana, Vol. I. 

 pp. 232 and 233. The former was taken in the Padauiri and the latter 

 in the Rio Branco, both of the Amazon basin. 



Key to the Genera of the Serrasalmin.b. 



a. Teeth symmetric, notched, or denticulate; no teeth on the palate; adipose fin 



not rayed, anal long, naked Pygopristis Miiller & Troschel. I. 



aa. Teeth oblique; asymmetric incisors, with a cusp on one or both sides near the 

 base of the large median cusp; successive teeth interlocking so as to form a 

 continuod? serrate cutting edge. 



b. Palatines smooth, without teeth; second suborbital covering all, or 

 nearly all, of the cheek; snout short, mouth wide; margin of upper jaw 

 very oblique; lower jaw very heavy, the teeth pointing backward and 

 upward, larger than those of the upper jaw. Interorbital 2-2.25 in 

 the head; depth 1.8-2 in the length. 

 c. Anal short, with fifteen rays, its origin below the space between dorsal 

 and adipose; no teeth on the palate. . . .Gastropristis gen. nov\ II. 

 cc. Anal with twenty-three tD thirty-eight rays; its origin below the dorsal. 

 d. Adipose fin rayed in the adult (normal in the young and half- 

 grown) Pygocentrus Miiller & Troschel. III. 



dd. Adipose fin not rayed Roosevelt iella gen. nov. IV. 



bb. Palate rough, or with obsolescent teeth (see under aureus) ; second sub- 

 orbital leaving a very wide naked area; margin of upper jaw not very 

 oblique; interorbital 2.25; depth 1.4-1.8 in the length to the end of 



the lateral line Prislobrycon gen. nov. V. 



bbb. A series of well-developed teeth on the palate; gape long, second sub- 

 orbital leaving a variable naked area, or completely covering the cheek; 

 upper jaw not very oblique Serrasalmo Lacepede. VI. 



I. Genus Pygopristis Miiller & Troschel. 



Pygopristis MiJXLER & Troschel, Hora? IchthyoL, Vol. I, 1845, p. 21, tab. ix, 

 figs. 2a and 26 {fujnarius). 



Type, Pygopristis fumarius Miiller & Troschel, = Serrasalmo den- 

 ticulatiis Cuvier. 



Characters of the Subfamily. — No teeth on the palate, those of both 

 jaws serrate or lobed; anal naked. 



Distribution. — Guiana to Paraguay. 



Key to the Species of Pygopristis. 

 a. D. 19; A. 35; depth 1.66; head 4; snout obtuse, as long as eye; second sub- 

 orbital reaching about half-way to the pre-opercle; about thirty to thirty-four 



abdominal serrae; adipose 3.5 in the dorsal denticulatus (Cuvier). i. 



aa. D. 16; A. 33; depth 1.66; adipose fin small; vertical fins with blackish margins. 



serridatiis Cuvier & \'alenciennes. 2 



