THE CHAR ACID AE. 21 



The scales, large or small, are ciliated in certain genera — a character very rare among 

 the Physostomes. As Valenciennes says of Distichodus, the free part of the scales is truly 

 ctenoid, the rest cycloid. The head always lacks scales, a rare thing in fishes. The lateral 

 line organ is represented on the opercle by a branch from the suborbital. 



The air-bladder is always divided into two parts by a constriction. The anterior part 

 is much smaller than the posterior. In some, Alestes, the air-bladder may be prolonged along 

 the right side of the hemapophyses and interneurals as far as the posterior end of the anal. 



There are generally 10-25 coeca on the stomach and this number may be raised to 35 

 or 40 (Hydrocyon, Citharinus). The intestine in the carnivorous genera is short and makes 

 but one loop; on the other hand, it is excessively long and with many windings in the 

 herbivorous types. 



In looking over this review of the characters of the family of Characins it is seen that 

 there is none that taken alone and allowing for the exceptions, justifies its separation from the 

 Cyprinids. 



We are forced to content ourselves with a combination of characters, any one of which 

 taken by itself is insufficient. 



These words apply almost verbatim to the American members of the family. 



The American Characins range from the border of the United States to 

 some distance south of Buenos Aires. They form about one third of the entire 

 South American fresh-water fauna and have diverged in adaptation to diverse 

 food, diverse habitat, and diverse enemies to fill nearly every niche open to 

 fishes. The ends of the three lines of adaptation to different food give us mud- 

 eating forms, with long intestinal tract and no teeth, 1 flesh-eaters with shear- 

 like teeth that are able to cut their way out of nets, attack large fishes, horses, 

 and bathers, and conical-toothed forms with sharp, needle-like teeth and com- 

 paratively huge fangs. Greater diversity could scarcely be imagined, and one 

 is led to suspect that some of the forms are over-adapted. In their divergence 

 in form they have reached almost every conceivable shape, and have approached 

 or paralleled many members of the diverse families of North American fresh- 

 water fishes. Our shads and fresh-water herrings have their counterparts in 

 Elopomorphus, Potamorhina, and Psectrogaster, our salmons are paralleled by 

 Salminus and Catabasis, and our minnows by Astyanax and its relatives. It 

 takes but a slight flight of the imagination to detect the striking similarity of 

 Luciocharax to our gar pikes; our mullets are duplicated by Prochilodus; our 

 top minnows are mimicked by Nannostomus. Bivibranchia, a recent dis- 

 covery, shows a close similarity to Albula, and even our festive darters are 

 duplicated by members Characidium of this most remarkable family. 



This plasticity of the family in both America and Africa, and the apparent 

 if not real duplication of forms in the two continents, is the more remarkable 



1 The toothless forms are not represented in Africa where members of the Cyprinidae replace them. 



