254 PROCEEDINGS OF THE NATIONAL MUSEUM VOL, 96: 
angle of preoperculum by a wide naked space; depth about 2 to 2% in, 
total length; origin of dorsal nearer end of snout than base of caudal, 
slightly behind origin of pelvics; probably about 95 to 110 scales from. 
head to caudal base__..--____- Colossoma brachypomus (Cuvier) 
8b. Numerous supplementary scales, which may obscure primary ones; anal 
fin densely scaled in at least its basal half and with highest rays. 
posteriorly or of nearly equal length posteriorly and anteriorly 
(Mylossoma). 
10a. Length of anal hase 2% to 3% times in standard length; ventral serrae-. 
10 to 13 along midventral line behind base of pelvics then 7 to 10: 
pairs around vent; branched dorsal rays 14 to 16 and anal with 33: 
to 36; base of adipose fin 3% to 6 in that of dorsal. 
Mylossoma acanthogaster (Valenciennes) 
10b. Length of anal base 1% to 2%4 in standard length. 
lla. Ventral serrae 10 to 15 behind root of pelvic fin; a space equal to. 
about one-fourth diameter of eye between last spine and first anal 
ray; dorsai with 14 to 16 branched rays, anal with 28 to 34; base. 
of adipose fin 3% to 4% in that of rayed dorsal. 
Mylossoma aureum (Agassiz) 
11b. Ventral serrae 18 to 22 behind root of pelvic; last spine very close. 
to first ray of anal; dorsal with 14 or 15 branched rays and anal 
with 34 to 38; base of adipose fin 2% to 224 in that of rayed dorsal.. 
Mylossoma duriventris (Cuvier) 
7b. A predorsal spine present; base of adipose fin less than half as long as that 
of rayed dorsal; dorsal with 22 rays or more; anterior teeth of outer se- 
ries of premaxillary with an oblique cutting edge, not greatly compressed, 
generally more or less separated from those of inner series (Myloplus). 
12a. Sides of body with more or less distinct round orange spots; margins. 
of anterior part of anal dusky; ventral serrae 28 + 10; dorsal iii or iv,,. 
24 to 28, anal ili or iv, 34 to 37. 
Myloplus asterias (Miller and Troschel) 
12b. A black vertical bar or blotch on side of body between dorsal and pelvic 
HN SWAN aly2 sto) 2am sae eee Myloplus schomburgkii (Jardine) 
Genus SERRASALMUS Lacepéde 
Serrasalmus Laceprhpn, Histoire naturelle des poissons, vol. 5, p. 2838, 1803.. 
(Type, Salmo rhombeus Linnaeus.) 
SERRASALMUS NATTERERI (Kner) 
CARIBE 
Pygocentrus natterert KNER, Denkschr. Akad. Wiss. Wien, vol. 18, p. 36, pl. 3,. 
fig. 8, 1859. 
Serrasalmo natierert Peters, Monatsb. Akad. Wiss. Berlin, 1877, p. 472 (San 
Fernando de Apure, Yenezuela).—RGu1L, Fauna descriptiva de Venezuela,. 
p. 377, fig. 190, 1942 (Orinoco). 
Serrasalmo (Pygocentrus) notatus Lirkmn, Vid. Medd. Naturh. Foren. Kjgben-. 
havn, 1874, pts. 12-16, p. 238 (Caracas, Venezuela). 
Pygocentrus notatus EIGENMANN and E1GENMANN, Proc. U.S. Nat. Mus., vol. 14,. 
p. 60, 1891 (Venezuela). 
Pygocentrus stigmaterythraeus FowuEr, Proc. Acad. Nat. Sci. Philadelphia, vol. 63,. 
p. 424, 1911 (La Pedrita on Cafio Uracoa, Venezuela). 
Rooseveltiella stigmaterythraeus EIGENMANN, Ann. Carnegie Mus., vol. 9, p. 245,. 
1915 (La Pedrita on Cajfio Uracoa). 
