SOUTH AMERICAN NEMATOGNATHI. 467 



arched posteriorly. Occipital process acute, somewhat 

 attenuate, meeting the dorsal plate; the apex of the oc- 

 cipital process usually narrowly truncate, its margins 

 deeply concave, leaving a more convex and larger nu- 

 chal plate on either side than in C. elegans. Fontanel a 

 short groove between the frontals and the anterior part 

 of the occipital bone; usually shorter than the orbit in 

 the 6 , about equal to the orbit in the ? , the bones nearly 

 grown together, leaving a short, very narrow slit. Sub- 

 orbital bone nearly smooth, very broad, exceeding the 

 orbital diameter; head everywhere mailed except at tip 

 of snout. 



Inner rictal barbels extending backward about to pos- 

 terior rim of orbit; lower lip free, and with a pair of 

 barbels two-thirds as long as the orbit. 



Eye lateral, circular, 1J in the snout, 3J in the head, 2 

 in the interorbital. 



Mouth inferior, very small, the intermaxillaries vesti- 

 giary. 



Lateral scutes overlapping on the back behind the dor- 

 sal fin, 3-4 azygous plates before the adipose fin. 



Coracoid processes meeting evenly for their anterior 

 half, diverging backward. 



Distance of the dorsal spine from the snout 2-2| in the 

 length; the spine not flattened, smooth in front, mi- 

 nutely serrate behind, higher than the rays, 1-1| in the 

 head, the rays decreasing backward to the last, which is 

 2-2J in the spine. 



Spine of the adipose fin hispid on its basal margins 

 like the dorsal plates which precede it. 



Caudal forked, about 2| in the length. 



Anal rounded, higher than long, the first ray flattened 

 spine-like. 



Ventrals 1J 1J i n the head, the outer ray stiffened and 

 bristly. 



