468 PROCEEDINGS OF THE ACADEMY OF [Oct., 



Width of head 2^ in its length; interorbital space 4. Body com- 

 pressed with edges all more or less rounded. Head compressed, con- 

 vexly round or not especially broad above, and sides becoming con- 

 stricted below. Snout broader than long and surface convex. Teeth 

 in jaws rather weak, though well developed, compressed, uniserial 

 and bidentate. Tongue free and rounded as seen above. Interor- 

 bital space rather broad and slightly convex. Gill-opening forward 

 opposite anterior margin of eye. Rakers reduced as minute tuber- 

 cles, and filaments a trifle less than orbit. Lateral line with simple 

 tubes. Vent close in front of anal. Color in alcohol brownish, sides 

 and lower surface paler, inclining to whitish and all more or less 

 silvered. Lower surface of head also silvered. A pale or dull slaty 

 humeral blotch about size of pupil. A dull or pale dusky diffuse 

 blotch at base of caudal. Fins all pale brownish, dorsal and caudal 

 a trifle darker, and median rays of latter also pale dusky. Iris pale * 

 brassy. Length 2^ inches (caudal damaged). Type. 



SERRASALMIN^. 

 Pygocentrus piraya (Cuvier). 



Serrasalmo piraya Cope, Proc. Amer. Philos. Soc. Phila., XI, 1869-70 

 (August 19, 1870), p. 566. Para. De Schulte Buckow. 



Head 2f; depth If; D. I, ii, 12; A. iii, 29, i; abdominal serratures 32 

 to vent; scales about 75 in lateral line to base of caudal and about 8 

 more on latter; about 33 scales between origin of dorsal and lateral 

 line; about 28 scales between origin of anal and lateral line; about 46 

 scales before origin of dorsal; about 13 scales obliquely back from 

 origin of adipose fin to lateral line; width of head 2^ in its length; 

 mandible 2f ; pectoral If; ventral 2J; least depth of caudal peduncle 

 3f ; snout 4^ in head, measured from tip of upper jaw ; eye 3f ; maxillary 

 2^; interorbital space 3. In alcohol more or less uniform brownish, 

 margins of caudal broadly a little darker brownish. Iris brassy, 

 brownish above and below. Length 3^ inches. 



Pygocentrus nattereri Kner. 



Serrasalmo nattereri Cope, Proc. Acad. Nat. Sci. Phila., 1871 (1872), p. 292. 

 Between the mouth of the Rio Negro and the Peruvian Amazon or 

 Ucayale River. Robert Perkins. 



Head 2^ to 2f ; depth If to Ijl ; D. I, ii, 14, i to 16, i ; A. I, in, 25, i to 

 28, i; abdominal serratures 25 to 28; scales 72 to 86 in lateral line to 

 base of caudal and 5 to 10 more continued out on latter; 34 to 38 

 scales obliquely back from origin of dorsal to lateral line; 30 to 37 scales 

 between origin of anal and lateral line; 15 or 16 scales obliquely back 

 from adipose fin to lateral line; 50 to 54 scales before dorsal; mandible 



