50 THE AMERICAN CHARACIDAE. 



Key to the Genera. 



a. Upper lip covering the teeth of the premaxillary ; dentary with a single series of teeth. 

 b. Some or all of the teeth serrate or notched. 

 c. Gill-rakers setiform or branched. 

 d. Preventral area with a median series of scales or with normal scales irregularly arranged, or 

 more or less trenchant with the scales of the two sides bent over the middle. 

 e. Maxillary border a simple more or less pronounced curve, or with a break in the symi letry 

 of the curve at the end of the tooth bearing portion. 

 /. Caudal fin at least partly covered with small, normal scales. 



g. Lateral line complete (see also under Hemigrammus inconstans, Moenkhausia cotinho). 

 h. Predorsal area with a median series of scales which are not notably smaller than the 

 other scales; D. 10-11. 

 i. Anal with a basal sheath of scales, its margin straight or emarginate. 



j. Lateral line much decurved in front, frequently several odd scales in front 

 between it and the next regular series; depth at least half the length; pre- 

 ventral area flat with sharply bent scales on the sides; profile depressed over 

 the eyes; occipital crest 5 of the distance from its base to the dorsal; outer 

 series of premaxillary teeth complete; anal long . . 1. Tetragonoptcrus Cuvier. 

 jj. Lateral line little decurved, parallel with the row of scales below it. 



k. Scales crenulate; an enlarged scale on each side of the base of the occipital 



crest 2. Entomolepis Eigenmann. 



kk. Scales entire; no enlarged scale on sides of the occipital crest. 



{I. Preventral area trenchant Slichonodonlinae) . 



II. Preventral area rounded. 



(m. A procumbent predorsal spine Slethaprioninae). 



mm. No procumbent predorsal spine. 



n. Second suborbital leaving a naked area between it and the lower 

 limb of the preopercle; at least five teeth in the inner row of the 

 premaxillary; outer series of premaxillary teeth in a line parallel 

 with the inner series except that one tooth frequently retreats 



from the line of the others 3. Moenkhausia Eigenmann. 



nn. Second suborbital in contact with the subopereulum below; four 

 teeth in the inner row of the premaxillary. Similar to Brycon- 



amerieus 4. Knodus Eigenmann. 



ii. Anal scaled to near its tip; caudal unequally lobed; anal margin convex. 



5. Markiana Eigenmann. 



hh. Predorsal line largely naked, a few scales of the sides near the dorsal with their 



margins bent over the back; D. 11 or 12; ventrals in front of the dorsal; anal 



emarginate or rounded 6. Gymnocorymbus ' Eigenmann. 



gg. Lateral line incomplete. 



o. Lower caudal lobe much the longer; maxillary without teeth. 



7. Thayeria Eigenmann. 

 on. Caudal lobes equal or subequal. 



p. Maxillary with teeth along its entire length. 



8. Prislella Eigenmann. 

 pp. Maxillary teeth, if present, crowded on the upper anterior angle. 



9. Hemigrammus Gill. 

 ff. Caudal fin naked except at its base. 



1 Poptella (Slethaprioninae) is almost identical with this genus but contains a hidden predorsal spine. 



