THE AMERICAN TETRAGONOPTERINAE. 107 
Gill-rakers one fifth to two sevenths of the diameter of the orbit, about 
7 + 12. 
Seales closely imbricate, with few divergent striae; caudal lobes scaled for 
about half their length; anal with a sheath of a single row of scales in front; 
lateral line but little decurved, the rows of scales above and below it parallel 
with it; a well-developed axillary scale. 
Origin of dorsal about equidistant from tip of snout and base of caudal, 
its height three and a half in the length; caudal deeply forked, the lobes about 
three in the length; anal deeply emarginate, its origin behind the vertical from 
the last dorsal ray; pectorals and ventrals about the same length, about equal 
to the length of the head without the snout; ventrals not to anal, tips of pec- 
torals one or two scales from ventrals. 
No caudal spot; a very narrow silvery band overlying a narrow dark band 
which in some specimens becomes wider in front, sometimes expanded into a 
humeral spot over the fourth scale of the lateral line, continued across the upper 
part of the opercle and preopercle to the eye; a black line along the base of 
the anal, expanded into a broader spot above the base and in front of the first 
anal rays; middle anal rays dark; scales of the back margined with dusky, 
scales of the median line in front of the dorsal dark. 
The Rockstone specimens have the caudal rose colored in life, especially 
the upper lobe; those from Gluck Island have the adipose and upper caudal 
lobe rusty, anal lobe lemon-yellow, dorsal yellow in center, tinged with orange. 
Vertebrae 12 + 17. 
Posterior air-bladder long, banana-shaped; curved down behind to in 
front of the anal, its diameter but little less than that of the eye, its length at 
least twice that of the anterior air-bladder. Alimentary canal about equal to 
the length (without the caudal). 
28. MorNKHAUSIA CEROS Higenmann. 
Plate 9, fig. 2; Plate 101, fig. 1. 
Moenkhausia ceros E1GENMANN, Bull. M. C. Z., 1908, 52, p. 104 (Lake Hyanuary); Rept. Princeton 
univ. exped. Patagonia, 1910, 3, p. 438. 
Hasirat.— Amazon Basin. 
