252 PATAGONIAN EXPEDITIONS : ZOOLOGY. 



Order III. PLECTOSPONDYLI. 



Cope, Am. Assoc. Adv. Science, Indianapolis, 187 1, 332. 

 As stated ante, p. 238, this order falls naturally into three groups of 

 families which are considered suborders and distinguished as follows : 



a. Lower pharyngeals falciform, parallel with the gill arches, usually provided with teeth ; mouth 



more or less protracted, usually bordered by the premaxillaries only ; jaws toothless ; brain 



case produced between the orbits ; basis cranii simple ; no adipose. Evcntogtiathi. 



aa. Lower pharyngeals normal ; mouth not protracted ; teeth in the jaws or none ; brain case 



usually not produced between the orbits ; basis cranii double. 



b. Not eel-shaped ; vent submedian ; a dorsal fin and usually an adipose dorsal ; ventrals 

 abdominal ; mouth usually bordered by the premaxillary and maxillary, more rarely by 

 the premaxillary only. Hetcrognaihi. 



bb. Eel-shaped ; vent under the head or at throat ; dorsal obsolete ; ventrals wanting. 



Gyinnonoti. 



Of these suborders the Eventognathi belong to the northern hemisphere, 

 not a single species having reached South America through natural- 

 channels. 



The Gymnonoti are exclusively South American, reaching from Guate- 

 mala to La Plata. No species approach the Patagonian region. 



Suborder Heterognathl 



The Heterognathi are composed of one, possibly two families, the Ery- 

 thrinidcr, peculiar to South America and the CJiaracida, in South 

 America and tropical Africa. The EyythrinidcB are not known to extend 

 south of Buenos Aires. 



Family IV. CHARACID.E. 



Characim, Miiller, Archiv Naturgesch., 9, Jahrg., I, 323, 1843. 

 CharacinidcE, Richardson, Encycl. Brit, 8th ed., XII, 245, 1856. 

 Characinidcs, Giinther, Cat. Fish, Brit. Mus. V, 278, 1864. 

 Characidcc, Gill, Mem. Nat. Acad. Sci. VI, 131, 1893. 



The Chavacidce flourish in the tropical fresh-waters ; but one species 

 reaches as far north as the boundary of the United States. Of the Chara- 

 cidce inhabiting the fresh-waters of tropical America, numbering about 

 100 genera and nearly 500 species, only two reach with certainty the 

 region under consideration. Both of these belong to the Tetragon opterincs. 



