THE AMERICAN TETRAGONOPTERINAE. 189 
4- to 5-pointed teeth in a graduated series, the last followed by seven or eight 
minute conical teeth. 
Gill-rakers 7 or 8 + 12. 
Anal sheath short, consisting of 3 or 4 scales and covering the bases of the 
first 7 rays. Lateral line with pores on 6 to 13 scales; four specimens in 21008 
have lateral line complete. 
Origin of the dorsal equidistant from the snout and caudal, the penultimate 
ray one third of the longest which is 4 in the length. Caudal equal to the 
length of the head plus the length of the eye. Origin of the anal on the verti- 
cal from the last dorsal ray; anal emarginate. Origin of the ventrals on the 
vertical from the first or second scale in front of the dorsal. Ventrals just reach- 
ing the anal; pectoral lapping a little onto the ventrals. 
All of the fins hyaline except an occasional dim spot at the base of the 
caudal which never reaches the end of the caudal rays. A distinct silver lateral 
stripe subtending a very inconspicuous, narrow brown or black stripe. The 
scales of the lateral line and the series above and below it have iridescence. 
The scales over the body-cavity have a less pronounced blue iridescence. 
12. HyPHESSOBRYCON RIDDLEI (Meek). 
Plate 26, fig. 3; Plate 79, fig. 6, 14a. 
Hemigrammus riddlei Mrrx MS. ErcenMANN & Oct», Proc. U.S. N. M., 1907, 33, p. 13 (Los Castillas). 
Hyphessobrycon riddlei ErarNMANN, Rept. Princeton univ. exped. Patagonia, 1910, 3, p. 436; Mem. 
Carnegie mus., 1912, 5, p. 340. 
One specimen Type Field Museum 38 mm. Los Castillas Riddle 
Head 3.85; depth 2.66; D. 10; A. 19; scales 5-32 to 34-3.5; eye and 
interorbital equal, 2.9 in the head. 
Compressed; depth of head at the base of the occipital process 4.75 in the 
depth. Preventral region rounded, without regular and complete series of 
median scales. Predorsal region rounded, with complete median series of 
10 scales. 
Occipital process 7 in the distance between its base and the dorsal, bor- 
dered by 2.5 to 3 scales. Interorbital very slightly convex. Frontal fontanel 
triangular, very small, narrower than the parietal, and half the length of the 
parietal without the occipital groove. Second suborbital in contact with the 
preopercle. Mouth small. Maxillary very little shorter than the eye, 3 in 
the head. Mandible 2.1 in the head. Premaxillary with about ten very small 
