Series Ostariophysi 161 



four orders: Heterognathi, Eventognathi (Plectospondyli), Nema- 

 tognathi, and Gymnonoti. 



The Heterognathi. Of these the order of Heterognathi seems 

 to be the most primitive, but in some ways the most highly de- 

 veloped, showing fewer traits of degeneration than any of the 

 others. The presence of the adipose fin in this group and in 

 the catfishes seems to indicate some sort of real affinity with 

 the salmon-like forms, although there has been great change in 

 other regards. 



The order Heterognathi, or Characini (erepos, different ; yva- 

 8os, jaw), contains those Ostariophysi which retain the meso- 

 coracoid and are not eel-like, and which have the lower pharyn- 

 geals developed as in ordinary fishes. In most cases an adipose 

 fin is present and there are strong teeth in the jaws. There are 

 no pseudobranchias, and, as in the Cyprinidce, usually but three 

 branchiostegals. The CharacidcB constitute the majority of the 

 fresh-water fishes in those regions which have neither Cyprinidce 

 nor SalmonidcB. Nearly four hundred species are known from 

 the rivers of South America and Africa. A single species, 

 Tetragonopterus argentatus, extends its range northward to the 

 Rio Grande in Texas. None are found in Asia, Europe, or, with 

 this single exception, in the United States. Most of them are 

 small fishes with deep bodies and very sharp, serrated, incisor- 

 like teeth. Some are- as innocuous as minnows, which they very 

 much resemble, but others are extremely voracious and destruc- 

 tive in the highest degree. Of the caribe, belonging to the 

 genus Serrasalmo, known by its serrated belly, Dr. Giinther 

 observes : 



"Their voracity, fearlessness and number render them a 

 perfect pest in many rivers of tropical America. In all the 

 teeth are strong, short, sharp, sometimes lobed incisors, arranged 

 in one or more series; by means of them they cut off a mouth- 

 ful of flesh as with a pair of scissors; and any animal falling 

 into the water where these fish abound is immediately attacked 

 and cut to pieces in an incredibly short time. They assail 

 persons entering the water, inflicting dangerous wounds before 

 the victims are able to make their escape. In some localities 

 it is scarcely possible to catch fishes with the hook and line, as 

 the fish hooked is immediately attacked by the 'caribe' (as 



ii ii 



