THE AMERICAN TETRAGONOPTERINAE. 87 



the young, shorter in adult, pectorals to ventrals or the width of one scale farther 

 in young, not to ventrals in the largest. 



A round humeral spot over the third to fifth scales of the lateral line, dis- 

 appearing with age; no caudal spot in adult, sometimes a dusky area at end 

 of caudal peduncle in young; a distinct silvery lateral band, the width of the 

 free margin of a row of scales; fins all plain, mostly hyaline; sides silvery, highly 

 iridescent. 



Air-bladder slender, not bent down behind to the anal, posterior section 

 not twice as long as the anterior, abruptly narrowed behind; diameter at its 

 widest part about equal to the eye. Alimentary canal about one and one third 

 times the entire length with the caudal; intestines containing insects and vege- 

 table fibers. 



Vertebrae 11 + 18. Tip of occipital process not extending beyond the 

 posterior face of the skull. 



As stated above, specimens from Obidos are distinctly more elongate than 

 others, whereas the largest specimen, the one from Cangaruma, is more than 

 half as deep as long. 



12. Moenkhausia ovalis (Gunther). 

 Plate 7, fig. 3. 



Tetragonoplerus ovalis Gunther, Proc. Zool. soc. Lond., 1868, p. 245 (Xeberos) ; Eigenmann & Eigen- 

 mann, Proc. U. S. N. M., 1891, 14, p. 53; Ulbey, Ann. N. Y. acad. sci., 1895, 8, p. 282; Fowler, 

 Proc. Acad. nat. sci., Phil., 1906, p. 441, fig. 38 (Maraflon); Regan, Ann. mag. nat. hist., 1913, ser. 

 8, 12, 281 (Ucayali). 



Tetragonoplerus clialceus Cope, Proc. Amer. philos. soc, 1878, 17, p. 691 (Maraflon). 



Moenkhausia ovalis Eigenmann, Rept. Princeton univ. exped. Patagonia, 1910, 3, p. 437. 



Habitat. — Maraflon. 



I have examined the type in the British Museum, represented in Plate 7, 

 figure 2. It is evidently closely related to M. grandisquamis. 



Head 3.66; depth 2; D. 11; A. 27; scales 5-31-4 (6 to anal). Eye 3 in 

 the head, 1.33 in interorbital. 



Upper profile rather more convex than the lower, scarcely concave at the 

 nape; preventral area flat; maxillary with two teeth, extending somewhat 

 beyond front margin of the eye; origin of dorsal just behind origin of ventrals; 

 pectoral extending beyond the ventrals, ventrals to the vent. Humeral spot 

 indistinct, caudal spot diffuse, extending over the base of the fin, not to the end 

 of the middle rays. 



