54 THE AMERICAN CHARACIDAE. 



1. Tetragonopterus Cuvier. 



rerpas four, yuwla angle, TTTepoe, to, wing = square winged. 



Tetragonopterus Artedi, Seba, Locupl. rerum, 1758, 3, pi. 34, fig. 3, (argenteus). 



Tetragonopterus Cuvier, Regne animal, 1817, 2, p. 166, (argenteus). Eigenmann, Rept. Princeton univ. 

 exped. Patagonia, 1910, 3, p. 438. 



Type. — Tetragonopterus argenteus Cuvier. 



Small fishes, pug-nosed, much compressed and very deep, the depth at least 

 half the length; humped at the occiput, concave over the eyes; interorbital 

 broad, rounded; snout very short, the maxillary nearly vertical; nostrils sepa- 

 rated by a valve; a long frontal fontanel extending beyond middle of eye; 

 parietal fontanel continued as a groove to the tip of the occipital crest, which 

 reaches £ to the dorsal; cheek largely covered by the suborbital; opercle very 

 short (nearly four times as high as long, in the type) ; premaxillary teeth in two 

 rows, the teeth of the outer series small, of nearly uniform size, the row more 

 or less regular, the teeth of the inner series larger, graduated, multicuspid, the 

 cusps of each tooth arranged in a curve, the middle cusp much the longest; 

 several large, graduated, several pointed teeth in the front of the lower jaw, 

 abruptly minute teeth on the sides; maxillary with or without teeth on its upper 

 anterior edge; gill-membranes entirely free from the isthmus; gill-rakers long, 

 slender; fins all well developed, the anal long, 32-37; scales entire, large on 

 the middle of the sides, becoming smaller in all directions, notably toward front 

 of anal 1 ; lateral fine complete, much decurved, several scales between its 

 origin and that of the regular series below it, caudal scaled; preventral area flat, 

 bounded by sharp angles, a median series of scales on the breast; seven or more 

 series of scales between the lateral line and the dorsal; postventral surface 

 trenchant; tongue thick, but little free. 



Vertebrae 10 + 19; alimentary canal about 1.4 the length over all. 



This genus, most nearly allied to Moenkhausia, is readily distinguished 

 from it by the greatly decurved lateral fine which is not parallel with the row 

 of scales' below it in front. 



Habitat. — Orinoco and Guianas, Amazons and south to Rio de Janeiro 

 and La Plata. 



1 In a specimen of T. argenteus the exposed edge of the 9th scale of the lateral line is about twice 

 as high as the exposed edge of the 4th, equal to two scales just below the beginning of the dorsal, greater 

 than the width of the flat ventral surface, equal to the scales of the lateral line plus the series above and 

 below it on the caudal peduncle, or equal to | the depth of the caudal peduncle. 



