THE AMERICAN TETRAGONOPTERINAE. 233 



Most closely related to Ctenobrycon hauxwellianus, but with a naked pre- 

 dorsal line, the young more slender, the scales on the sides below the lateral line 

 less regularly arranged. This species is evidently the southern modification of 

 C. hauxwellianus. 



Head about 4; depth 2-2.2; D. 11; A. 40-45; scales 11-48 to 50-8; eye 

 2.75; interorbital 2.5, in the largest 2.75. 



Compressed, elongate; ventral profile from snout to end of anal, a nearly 

 regular arc of a circle with a diameter of a little more than half the length; 

 dorsal profile equally arched but the outline less regular, being, with age, increas- 

 ingly humped in the nape. Preventral area rounded, without a median series 

 of scales; postventral area bluntly keeled. Predorsal area bluntly keeled, 

 with a double series of half scales which do not meet over the back; 7-9 scales 

 along either side of the occipital process. 



Occipital process about one third of the distance from its base to the dorsal. 

 Frontal fontanel more than half the length of the parietal which is continued 

 as a groove to the tip of the occipital process. Interorbital convex. Second 

 suborbital leaving a naked area of equal width aroimd its entire free margin. 

 Mouth minute, the maxillary very convex in front, nearly vertical, its length 

 equals that of snout in medium sized specimens, less than snout in the largest, 

 4-5 in the head ; four or five teeth in the front row of the premaxillary, five in the 

 second row; a single, broad tooth on the maxillffry. 



Gill-rakers 10 -|- 17, the longest not equal to one third the length of the eye. 



Scales ciliate in the adult, entire in the young, with numerous radiating 

 striae, regularly imbricate but irregular in size above the lateral line. Lateral 

 line nearly straight, the row of scales below it dicotomously branched above the 

 origin of the ventrals, the main row being apparently deflected; other rows 

 similarly branched. The rows of scales above the front of the anal are all 

 oblique; from above the second third of the anal, there are two or thi'ee series 

 of scales parallel with the lateral line; scales becoming smaller backward; the 

 ventrals and origin of anal, being equally removed from the lateral line, have 

 respectively 9 and 14 rows of scales or 8 and 13. Anal sheath continued with the 

 scales of the sides, of three rows of scales. Caudal naked; a large axillary scale. 



Origin of dorsal equidistant from tip of snout and base of caudal or a little 

 nearer the latter; dorsal pointed, its rays rapidly and regularly graduate, the 

 highest three in the length, the penultimate not much more than one third the 

 length of the highest. Origin of anal and base of last or middle dorsal ray 

 equidistant from snout, its margin nearly straight; fifth to seventh scale in front 

 of dorsal and ventrals eqmdistant from tip of snout, reaching to anal in young 



