SOUTH AMERICAN NEMATOGNATHI. 453 



Callichthys affinis Giinther was separated from C. cal- 

 lichthys on the number of lateral plates. The usual num- 

 ber is |4, but we have examined specimens from Rio 

 Janeiro with plates TJ-|_|- T . As these specimens are in- 

 termediate between callichthys and affinis, we have placed 

 the latter in the synonymy. 



Depth below dorsal spine equal to the width; body com- 

 pressed backward. Head short, depressed, flat above; 

 its width greater than its length; its depth 1J- in its 

 length; profile steep; fontanel circular; snout and cheeks 

 naked; suborbital bones covered with skin; opercle with 

 a marginal group of short, slender bristles. 



Eye very small, about .equal to the fontanel, 4 in the 

 snout, 10 in length of head, 7 in the interorbital space. 



Inner rictal barbels longer than the upper, reaching 

 the base or beyond the tip of the humeral process. Nares 

 less than, or about 1 orbital diameter apart, the poste- 

 rior 1 diameter or less from the eye. 



Snout narrowly rounded in front. 



Mouth terminal, lower lip with a broad free margin 

 and an incision at the symphysis. Intermaxillaries 

 rudimentary, toothless. An elongate patch of brown- 

 tipped teeth on the sides of the lower jaw. 



Gill-openings rather wide, extending under the throat. 



Lateral plates covering the entire sides of the body, 

 their posterior margins with fine bristles; a narrow naked 

 area along the back, extending forward on the sides of 

 the base of the dorsal fin, and forming a triangular 

 naked area in front of it; a series of deeply pectinate, 

 scale-like plates in front of the adipose fin, not meeting 

 the lateral plates; a naked strip along the sides of the 

 adipose fin. 



The lower surface of the coracoid process entirely con- 

 cealed by skin in the adult. 



Rays on the sides of the unpaired fins, and on the 



