238 PATAGONIAN EXPEDITIONS : ZOOLOGY. 



Superorder Ostariophysi. 



Ostayiophysi Sagemehl, Morph. Jahrbuch X, 1-120, plates I and II. 



Anterior four vertebrae coossified, much modified ; frequently a chain of 

 four ossicula auditus forming the Weberian apparatus attached to the 

 anterior vertebrae and connecting the air-bladder with the auditory appa- 

 ratus ; air-bladder connected with the alimentary canal by a duct. Parie- 

 tals separating the frontals from the supraoccipital or fused with the latter. 

 Shoulder girdle suspended from the skull by a long post temporal ; meso- 

 coracoid arch well developed ; opercle well developed. Ventrals abdomi- 

 nal, without spines. 



The fishes belonging to the families making up the order or superorder 

 of Ostariophysi are the dominant forms in the fresh waters of the world. 

 They fall naturally into two groups or orders : 



I. Nematognathi with no subopercle or symplectic bone ; the supra- 

 occipital and parietals coossified ; the maxillary usually without teeth and 

 reduced to form the core of a variously developed barbel ; no scales. 



II. Plectospondyli, a less solid group ; with subopercle and symplectic 

 bones and with a well formed maxillary and frequently with teeth. 



Of these the Nematognathi are found both in the northern and south- 

 ern hemispheres and have also become inhabitants of the sea. 



The Plectospondyli fall into three groups of familes, those related to 

 the Cyprinidce, confined chiefly to the northern hemisphere but overflow- 

 ing into northern Africa, those related to the CharacidcB inhabiting Africa 

 and South America but overflowing into Central America and Mexico, and 

 those related to the Gyniuotidcc and confined to tropical America. 



Of the 1,200 or more species of fresh-water fishes recorded from tropical 

 America, about 1,000 belong to the Ostariophysi; in round numbers about 

 500 of these belong to the Nematognathi and another 500 to the Plecto- 

 spondyli. Of the African fresh-water fishes a much smaller per cent, are 

 Ostariophysi. 



Of this vast array of American species, very few are found within the 

 boundaries of the region under consideration and most of these barely 

 cross its northern border. 



