THE AMERICAN TETRAGONOPTERINAE. 93 



Head, 3.7-3.8; depth 2.5-2.7; D. 10; A. 26; scales 5-34-3 or 4. Eye 2.1; 

 interorbital 2.4 or 2.5. 



Elongate, subrhomboidal, the ventral surface in front of the anal distinctly 

 arched; a very slight depression over the eye; preventral area rounded, a series 

 of median scales; postventral region narrowly rounded, with a median series of 

 large scales, bordered by slightly asymmetrical scales. Predorsal area keeled 

 to near the occipital crest. A median series of scales between the dorsal and 

 occipital crest whose length is about one fifth of the distance from its base to the 

 dorsal. 



Interorbital slightly convex; second suborbital leaving a narrow naked 

 border on the cheek. Maxillary three in the head; four or five teeth in the front 

 row of the premaxillary, the third somewhat removed from the rest; five grad- 

 uated teeth on the inner row; two small teeth on the maxillary; mandible with 

 four large teeth and numerous small ones on the side. 



Gill-rakers about 9 + 12. 



Scales regularly and deeply imbricate, each with several divergent striae. 

 Anal sheath of a few scales in a single row near front of anal; lateral line but little 

 decurved; caudal scaled for about one fourth of its length. 



Origin of dorsal in front of middle of body, but little more remote from snout 

 than dorsal; highest dorsal ray about two and two thirds in the length; caudal 

 deeply forked, the lobes longer than the dorsal; anal deeply emarginate; ven- 

 trals not reaching anal, pectorals just to ventrals. 



No humeral spot; caudal with a small diffuse dark spot at the base of the 

 middle rays. Scales of sides margined with dark, the marginal spots tending 

 to form lines along the sides; pigment more profuse toward the back; a series 

 of dark spots on the median series of scales of the back. 



18. Moenkhausia costae (Steindachner). 

 Plate 14, fig. 2; Plate 100, fig. 2. 



Telragonoplerus costae Steindachner, Anz. K. akad. wiss. Wien, 1907, p. 83 (Rio San Francisco; Rio 

 Grande do Norte; Rio Preto). 



Habitat. — Rio San Francisco; Rio Itapicuru. 



