240 Annals of the Carnegie Museum. 



Head 3-3.6 in length to end of lateral line; depth 1.8-2; D. 18-19; 

 A. 30-32; serrse 22-26; interorbital 2-2.25 ii^ the head (nearly 3 in 

 No. 5696). 



Base of anal shorter than head; distance between dorsal and caudal 

 fulcra shorter than the dorsal, equal to, or a little shorter than, the 

 postorbital portion of the head (postorbital portion and half the eye in 

 No. 5696); dorsal rounded; adipose fin not rayed in specimens 130 mm. 

 long. Sides plain in specimens 100 mm. long; entire sides profusely 

 spotted in specimens below 60 mm. long. 



Dr. J. D. Anisits has kindly furnished me with the following data 

 -on the Pygocentriis nigricans in the Berlin Museum. 



No. 3630 Berlin Museum. Total length 122 mm., body 112 mm., 

 height 61 mm. Head 3 in the length; eye 4.33 in the head, 2.66 in the 

 interorbital; abdominal spines 28; D. 16; A. 31; scales 34-104-39. 

 The photograph kindly made for me by the direction of Dr. A. Brauer, 

 Director of the Zoological Museum of Berlin, shows the distance 

 between the dorsal and caudal to be greater than the length of the 

 dorsal and longer than the postorbital portion of the head. It seems 

 more than probable that the nigricans of M tiller and Troschel is 

 .distinct from piraya Cuvier. 



Lutken (Vidensk. Medd. Nat. For. Kjobenhavn, 1874, 238) con- 

 siders the nigricans of Agassiz a species distinct from piraya. 



IV. Genus Rooseveltiella^ gen. no v. 



Type, Serrasalmo nattereri Kner. 



General characters of Pygocentrus, the adipose fin not rayed; palate 

 without teeth, smooth; cheek completely or nearly completely armed 

 in adult; profile scarcely depressed over the eye; eye comparatively 

 small; interorbital very wide; upper jaw short, its margin very oblique; 

 lower jaw powerful, its teeth long, with nearly symmetric cutting 

 edges, much larger than those of the upper jaw. 



Distribution. — Orinoco, Guianas, Amazons, and La Plata basin. 

 Not in the Rio San Francisco and coastwise streams south to Rio 

 Grande do Sul. 



It is doubtful whether niger, altiis, and nattereri are distinct. It is 

 also quite probable that stigrnaterythrceus is a synonym of notatiis. 



* For Colonel Theodore Roosevelt in recognition of his arduous work in South 

 American Exploration and his intense interest in the fauna of South America. 

 His account of the type of this genus was quoted on previous pages. 



