THE AMERICAN TETRAGONOPTERINAE. 239 



Distinguishable from all other members of the genus by the triangular, 

 asymmetrically placed caudal spot. 



Head 3.3-3.7; depth 3-3.3; D. 11; A. 30, 32, 28; scales 11 or 12-54 or 

 55-9; eye 2.5-2.75 in the head; interorbital 3.1-3.75. 



Compressed, symmetrically elliptical to the slender caudal peduncle. Pre- 

 ventral area flattened, with a distinct median series of scales for at least part 

 of the length; postventral area compressed to an edge. Predorsal area com- 

 pressed, without a median series of scales, the scales of the sides not bent over 

 the ridge, which is naked. 



Occipital process about one fourth the distance of its base from the dorsal, 

 bordered by about 6 scales on each side. Frontal fontanel but little shorter 

 than the posterior, exclusive of the groove on the occipital process. Inter- 

 orbital but little convex. Second suborbital quite or nearly in contact with the 

 vertical limb of the preopercle behind, but leaving a considerable naked area 

 below. Snout long and pointed. Maxillary long and slender, about as long 

 as the eye. Three or four teeth in the front row of the pre maxillary, if four 

 the third removed from the line; five teeth in the second series, the denticles 

 arranged in a nearly straight line. Two very minute teeth on the maxillary. 

 Dentary with four slightly graduate teeth and a number of smaller ones. Man- 

 dibles half the length of the head. 



Gill-rakers slender, a little more than one third diameter of eye, about 8 + 

 14. 



Scales small, cycloid, with numerous concentric lines but few radial striae, 

 every^vhere very regularly but not deeply imbricate, of nearly uniform size; 

 caudal naked. Anal sheath composed of a single series of caducous scales. 

 Lateral line Uttle decurved, the row of scales below it parallel with it ; no inter- 

 polated scales even over the anal muscles; axillary scale well developed. 



Origin of dorsal a scarcely perceptible distance nearer tip of snout than 

 base of caudal, pointed, its highest ray about 3.5 in the length. Caudal lobes 

 a little longer than the highest dorsal ray. Anal emarginate, the highest ray 

 about 6 in the length; the 12th ray about half the length of the highest; origin 

 of anal and base of last dorsal ray equidistant from tip of snout. The ventrals 

 reaching anal, scarcely nearer tip of snout than to the base of the first dorsal ray. 



All but the tips of the middle caudal rays black, the spot continued obliquely 

 downward on the end of the caudal peduncle to its lower edge, otherwise immacu- 

 late. 



