Eigenmann: The Serrasalmin.^ and Mylin/e. 261 



dorsal comparatively long;; ventrals minute; anal long; adipose 

 variously developed; gill-rakers well developed. 



Key to Genera of Mylin^. 

 a. Teeth thorn-like, wide set and almost concealed by the lips and gums; pre- 

 maxillary with two antrorse, large teeth in the front series and three smaller 

 ones in the second series; no inner teeth in the lower jaw; mouth very 

 oblique, lower jaw inordinately projecting; a predorsal spine; serrae along 

 the ventral edge from below the pectorals to the anal; adipose large; cheeks 



entirely mailed Caloprion Miiller & Troschel. i. 



aa. Teeth incisors or molars, not antrorse; lower jaw not much projecting, or the 

 jaws equal, the mouth nearly horizontal; two teeth in the second transverse 

 row of the premaxillary, five teeth in the front row, which may be continuous 

 or broken, the teeth arranged stepwise from the last on the sides to the first 

 in front. 



b. Mandibles without an inner pair of teeth; abdomen serrate behind the 

 ventrals, smooth in front of them. 



c. Dorsal rays prolonged, filiform; anal in male bilobed. 



Mylesinus Cuvier & Valenciennes. 2. 

 cc. Dorsal rays scarcely prolonged, the margin of the fin oblique, not 



falcate; gill-rakers filamentous Acnodon Eigenmann. 3. 



bb. Mandibles with a pair of teeth behind the symphyseal pair; abdomen with 

 serrae in front, as well as behind the ventrals; second suborbital leav- 

 ing a wide naked area. 



d. No predorsal spine. 



e. No supplementary scales; anal naked, as long as head or shorter, 

 highest in front, without distinct lobes. 

 /. Adipose dorsal rayed; opercle with a broad membranous 

 border; gill-rakers numerous, very fine. 



Piaractus Eigenmann. 4. 

 //. Adipose dorsal not rayed. Opercle with a narrow mem- 

 brane Colosoma Eigenmann. 5. 



ee. Numerous supplementary scales obscuring the primary ones and 

 giving the surface a velvety texture; free margin of anal con- 

 vex, the posterior part highest; anal scaled for at least half 

 of its height, much longer than head; opercles with a narrow 

 lobe; gill-rakers moderate in number and size. 



Mylosoma Eigenmann. 6. 

 g. Abdomen not excessively pendant. . {Mylosoma Eigenmann.) 

 gg. Abdomen excessively pendant, depth about 1.14. 



{Slarksina Fowler.) 

 dd. A predorsal spine. 



h. Adipose fin long, more than half the length of the dorsal; dorsal 

 with fewer than 20 rays; free margin of anal slightly convex 



or with a single lobe in front Metynnis Cope. 7- 



i. Gill-rakers long, setiform {Metynnis Cope.) 



a. Gill-rakers equal to half the length of the eye or shorter. 



{Sealeina Fowler.) 



