SOUTH AMERICAN NEMATOGNATHI. 227 



sometimes are joined in front partially surrounding the 

 adipose fin. The dorsal plates vary independently of the 

 size of the fish and sometimes they are entirely absent; 

 those in front of the adipose fin are sometimes large, 

 while there are none behind it and the reverse is some- 

 times true. Lower surface of the caudal peduncle and 

 sometimes the region hehind the ventrals with a series 

 of plates similar to those on the back. 



Humeral process narrow and pointed, reaching a little 

 beyond the middle of the pectoral spine, its surface 

 simply granular without ridges or spines. 



Distance of the dorsal spine from the snout 2i to 2| 

 in the length; dorsal spine about as long as the head; 

 serrated on both margins, the spines of the anterior 

 margin becoming larger and fewer towards the tip, but 

 not as large as the corresponding ones on the posterior 

 margin; the serrations stronger than in any other 

 species of this genus; sides of the spine striate. Distance 

 of the adipose fin from the dorsal fin 31-41 in the 

 length; adipose fin oval, much shorter than the dorsal 

 fin. Caudal deeply forked, 83-4 in the length. 



Anal fin truncate, the fifth ray highest, 1| in the 

 head. 



Pectoral spine strong, straightish, reaching to the 

 fifth or sixth lateral scute; its margins with fewer but 

 stronger serrse than the other species of the genus; pec- 

 toral pore very small. 



Region above the lateral scutes brown, region below 

 them lighter; sides of the head and anterior portion of 

 the body with minute dark dots. Fins all more or less 

 dusky; lobes of the caudal fin yellow, middle rays dark 

 brown; anal sometimes with a dark spot at its base. 



Head 4i ; depth 4-5; Lat. 1. 16-20; D. I, 6; A. 13 or 

 14; V. 7; P.I, 8. 



