402 CALIFORNIA ACADEMY OF SCIENCES. 



Two specimens about .57 m. long from Manacapuru, 

 ? , 3 , have the tip of the snout granular; the occipital 

 ridge more prominent in the male than in the female; 

 the nuchal plates obtusely bicarinate in both, the lateral 

 plates slightly more carinate in the male; the pectoral 

 spine not reaching the ventrals in either; pectoral spine 

 and outer caudal rays bristly in both, the bristles in the 

 male being about twice as long as in the female. 



The male is much lighter colored than the female. 



Elongate, slender; head pointed; occipital with a nar- 

 row keel. Blunt ridges from the anterior nares to the 

 occiput. Superciliary margin raised; occipital mar- 

 gined with several small nuchal plates, which, with age, 

 become united with the occipital, making its posterior 

 edge appear emarginate. 



Humeral ridge becoming strongest on the caudal por- 

 tion of the body, margining the flat lower surface of the 

 tail; other scutes more weakly or not at all keeled. A 

 conspicuous plate before the anal fin. 



Tip of snout naked, rarely granular. 



Eye 4-5i in the snout, 7-9 \ in the head, 3-3 J- in the 

 interorbital. 



Ventral surface, except a small space in front of the 

 ventrals, entirely covered with small scales. 



Base of the dorsal fin less than its distance from the 

 adipose fin. 



Outer caudal rays greatly produced, comparatively 

 shorter in the adult and with numerous long bristles. 

 Pectoral spines in the adult with similar but much longer 

 bristles than those on the caudal fin. 



Straw color or ashy, roundish dark spots on the dorsal 

 surface, smallest on the head, sometimes confluent into 

 vermiculations, especially in the adult; fins all spotted 

 or with irregular cross bars, the markings least distinct 

 on the caudal; ventral surface usually plain. 



