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12b. Fourth gill arch normal. 
13a. Nostrils close together and separated only by a dermal flap; 4 
teeth with broad cutting edges projecting forward in each 
side of both jaws; basal two-thirds of caudal lobes scaled; 
lips reflected with a free margin on both jaws, the lower lip 
lobed; anal short, without basal sheath of scales. 
Leporellus Liitken (p. 265) 
13b. Nostrils rather widely separated by an isthmus of skin, the 
anterior nostril somewhat tubular; predorsal plate absent. 
14a. Mouth small, terminal, or inferior, with 4 to 6 teeth on each 
side of both jaws directed obliquely forward toward 
middle, these teeth obliquely truncate or lobed; anal 
short; snout conical; second suborbital not covering more 
_ than half of cheek; lips somewhat plicate. 
Leporinus Agassiz (p. 267) 
14b. Mouth opening vertical or nearly so, narrow and elongate, 
lower jaw folding upward to close mouth; lower jaw 
bearing at its tip 2 large, hooked, projecting teeth, sickle- 
shaped at tips; upper Jaw with 3 or 4 spear-shaped teeth 
on each side directed forward. 
Gnathodolus Myers (p. 268) 
14c. Mouth small, terminal or oblique, with incisorlike teeth 
lobed or not in a single series of 8 in each jaw, those at 
front of lower jaw not directed forward toward middle; 
lips not plicate. 
15a. Middle teeth of lower jaw trifid, with three points; 
mouth terminal, somewhat oblique (fig. 31, a). 
Schizodon Agassiz (p. 268) 
15b. Middle teeth of lower jaw incisors with truncate edge; 
mouth terminal, oblique--_-_- Laemolyta Cope (p. 272) 
11b. Gill membranes extending far forward and free from isthmus or 
16a. 
narrowly joined far forward, sometimes with a free fold across 
isthmus, or sometimes broadly joined to each other with a wide 
free fold across isthmus. 
Midline of belly with a keel or ridge in front of pelvics; abdominal 
region sometimes greatly compressed to an edge, or trenchant; 
anterior and posterior nasal openings close together, separated 
only by a dermal flap. 
17a. Lateral line complete. 
18a. Lateral line nearly straight along midaxis of body; mouth 
large, gape oblique, teeth conical, sharp, long canines 
present; gill membranes separated, free from isthmus. 
19a. Anal fin covered with minute scales nearly to their tips, 
caudal fin with minute scales basally; scales minute. 
20a. Dorsal origin considerably in front of anal origin. 
Hydrolycus Miller and Troschel (p. 272) 
20b. Dorsal origin behind anal origin and both far behind 
middle of elongate body; dorsal profile nearly 
straight, ventral profile curved to under pectorals, 
then nearly straight; belly much compressed, ventral 
edge! thing Wigan enki Rhaphiodon Agassiz (p. 273) 
19b. Anal base with a sheath of scales consisting of about 2 
rows; caudal fin base not with minute scales; anal rays 
iv, 40 to iv, 49; dorsal origin a little behind anal origin; 
