40 THE AMERICAN CHARACIDAE. 



The eyes are always large, the species depending largely on living and 

 moving food. The cheeks may be narrow or deep and are one third or entirely 

 covered by the second suborbitals. 



The premaxillary teeth are always in at least two series. The inner series 

 consists of from 4-12 graduated; three to many-pointed (a few may be conical) 

 teeth arranged in a regular series. The outer row is very variable both in the 

 group and in individual species and ranges from one or more teeth near the 

 middle of the premaxillary, to a complete, compact series of teeth, narrower 

 than those of the inner series in Tetragonopterus. If the outer row consists of 

 four or more teeth the third tooth usually drops out of line and tends to form a 

 third series of teeth. In Moenkhausia melanogramma the third tooth is entirely 

 withdrawn from the line of the others. In the related Brycon in which the 

 teeth are more numerous than in the genera of this subfamily, the fourth tooth 

 and a few others also drop out of line and join the third tooth of the lower inner 

 series which has moved forward. Other teeth of the inner series have also 

 moved forward giving rise to a third series of teeth. A third series of teeth has 

 independently arisen in Creagrutus and Bryconops, and in the Bryconinae. 



The maxillary may have no teeth, or a few may be crowded along the part 

 of the margin nearest to the premaxillary, or it may have conical or tricuspid 

 teeth along its entire margin. Usually the variation in any one species is very 

 limited, but in Astyanax fasciatus nicaraguensis there is a variation of from one 

 to nine teeth in the maxillary. 



The teeth in the lower jaw may all be alike and graduate, or the lateral 

 teeth may be more or less abruptly smaller, the more abruptly the more proba- 

 bly the lateral teeth will be conical. The larger teeth, 3-6 in number, may form 

 a nearly transverse series or be arranged in a curve. 



The denticles of the individual teeth of the inner series of the premaxillary 

 may be in a straight line, i. e., the teeth may be strictly incisors or, the line 

 joining the cusps may be more and more curved so that it will be U-shaped, 

 the open part of the U forward. The teeth in the lower jaw are usually the 

 reverse of those of the inner series of the upper jaw. 



Gill-rakers are usually slender and not very long, they are all but absent 

 in one genus, Scissor. The gill-membranes are free from each other, the nares 

 close together. The breast is flat or rounded, never keeled. The scales are 

 usually cycloid, rarely crenate or even ctenoid. They vary from 26 to about 

 60 in the lateral line, which is variously developed. 



The caudal may be naked, the scales of the sides passing on to its base and 



