1 a.	Inner base of pectoral densely covered with scales as shown in Figure 2. ……… 2

1 b.	Inner base of pectoral without scales, or with only a few scales. ……… 14
2 a.	A persistent large black blotch on side of body (Fig. 10). Lateral teeth of jaws include strong molars in adults. ……… 1. Lethrinus harak.

2 b.	Without such a blotch as in 2 a. ……… 3
3 a.	Second dorsal spine much longer than third. Usually five scale rows between lateral line and median dorsal spines. (The row on lateral line itself excluded.) Lateral teeth of jaws small and pointed. Posterior nostril much closer to anterior one than to orbit. ……… 2. Lethrinus nematacanthus.
3 b.	Second dorsal spine shorter than third. ……… 4
4 a.	Posterior nostril much closer to anterior one than to orbit. Lateral teeth of jaws include strong molars. ……… 3. Lethrinus sanguineus.
4 b.	Posterior nostril about halfway between anterior one and orbit. ……… 5
5 a.	Five scale rows between lateral line and median dorsal spines. ……… 6
5 b.	Six scale rows between lateral line and median dorsal spines. ……… 9
6 a.	Longest soft anal ray distinctly longer than base of soft anal. ……… 7
6 b.	Longest soft anal ray not longer than base of soft anal. ……… 8
7 a.	End of jaws usually on the vertical through anterior margin of orbit. All pelvic fin membranes with dense melanophores uniformly distributed on them as shown in Figure 4-A. Lateral teeth of jaws wide and roundish but not distinct molars. ……… 4. Lethrinus kallopterus.

7 b.	End of jaws on the vertical through posterior nostril. Pelvic fin membranes with fewer melanophores than in 7a, especially few on the inside of distal portion (Fig. 4-C). Lateral teeth of jaws include strong molars in adults. ……… 5. Lethrinus hypselopterus.
8 a.	All pelvic fin membranes with dense melanophores uniformly distributed on them as shown in Figure 4-A. Lateral teeth of jaws small and pointed. ……… 6. Lethrinus amamianus.
8 b.	Pelvic fin membranes with fewer melanophores than in 8a, especially few on the inside of distal portion (Fig. 4-C). Lateral teeth of jaws include strong molars in adults. ……… 7. Lethrinus mahsena.
9 a.	Pelvic fin membranes with dense melanophores uniformly distributed on them excepting the innermost area as shown in Figure 4-B. ……… 10
9 b.	Pelvic fin membranes with fewer melanophores than in 9a, especially few on the inside of distal portion (Fig. 4-C). ……… 11
10 a.	Body deep, 2.3-2.5 in standard length. ……… 8. Lethrinus anarhynchus.
10 b.	Body less deep, more than 2.5 in standard length. ……… 9. Lethrinus nebulosus.
11 a.	Snout length excluding upper lip distinctly more than cheek width. (For the method of measuring, see Fig. 6.). ……… 12

11 b.	Snout length excluding upper lip equal to or less than cheek width. Strong molars on side of jaws in adults. ……… 13
12 a.	Lateral teeth of jaws include strong molars in adults. Posterior end of operculum with a red spot. No conspicuous yellow stripes on body. ……… 10. Lethrinus opercularis.
12 b.	Lateral teeth of jaws include roundish but small ones, no distinct molars. Posterior end of operculum without red spots. Several bright yellow longitudinal stripes conspicuous on body. ……… 11. Lethrinus ramak.
13 a.	Posterior rims of preoperculum and operculum bright red. Several bright yellow longitudinal stripes conspicuous on body. ……… 12. Lethrinus ornatus.
13 b.	Posterior rim of only operculum bright red. No conspicuous yellow stripes on body. ……… 13. Lethrinus mahsenoides.
14 a.	Length from the anteriormost point of snout next to the lip to anterior nostril more than cheek width. (For the method of measuring, see Fig. 6.) Usually six scale rows between lateral line and median dorsal spines. (The row on lateral line itself excluded.). ……… 14. Lethrinus miniatus.
14 b.	Relationship of the above two lengths reversed. ……… 15
15 a.	Five scale rows between lateral line and median dorsal spines. ……… 16
15 b.	Six scale rows between lateral line and median dorsal spines. Strong molars on sides of jaws in adults. ……… 15. Lethrinus lentjan.
16 a.	Found in Atlantic Ocean. Lateral teeth of jaws conical or roundish but small. ……… 16. Lethrinus atlanticus.
16 b.	Found in Indo-Pacific. Lateral teeth of jaws conical. ……… 17
17 a.	Head length less than body depth. ……… 18
17 b.	Head length more than body depth. ……… 19
18 a.	All pelvic fin membranes with dense melanophores uniformly distributed on them as shown in Figure 4-A. ……… 17. Lethrinus chrysostomus.
18 b.	Pelvic fin membranes with fewer melanophores than in 18a, especially few on the inside of distal portion (Fig. 4-C). ……… 18. Lethrinus haematopterus.
19 a.	All pelvic fin membranes with dense melanophores uniformly distributed on them as shown in Fig. 4-A. ……… 20
19 b.	Pelvic fin membranes with fewer melanophores than in 19a, especially few on the inside of distal portion (Fig. 4-C). ……… 25
20 a.	Posterior nostril much closer to anterior one than to orbit. ……… 19. Lethrinus variegatus.
20 b.	Posterior nostril about halfway between anterior one and orbit. ……… 21
21 a.	Triangular scaleless area above pectoral base large, bright red when fresh (Fig.7). ……… 20. Lethrinus conchyliatus.

21 b.	The above area small, not red even when fresh. ……… 22
22 a.	Area without or with only a few melanophores, bright red when fresh, on outer pectoral base as shown in Figure 8. ……… 23

22 b.	No such area as in 22a. ……… 24
23 a.	Area without melanophores on the upper half of pectoral base (Fig. 8-A). ……… 21. Lethrinus xanthochilus.
23 b.	Area without melanophores wholly on pectoral base (Fig. 8-B). ……… 22. Lethrinus reticulatus.
24 a.	A few dark streaks from eye forward (Fig. 32). ……… 23. Lethrinus microdon.

24 b.	No such streaks as in 24a. ……… 24. Lethrinus amboinensis.
25 a.	Scaleless area, bright red when fresh, on posterior end of operculum as shown in Figure 9-A. ……… 25. Lethrinus rubrioperculatus, sp. nov.
25 b.	No scaleless area on posterior end of operculum, or not so clear as in 25a (Fig. 9-B). ……… 26. Lethrinus semicinctus.