Key to males of Largusoperla species (L. sp. is excluded)

1. Paraprocts distinctly asymmetrical, one paraproct larger, other smaller............................................ 2

-. Paraprocts symmetrical, shape of paraprocts similar.......................................................... 4

2. Paraprocts weakly sclerotized, subtriangular with sharp apex; left paraproct widened at mid-length, right paraproct constricted at mid-length............................................................................. L. difformitatem

-. Paraprocts partially sclerotized, apex blunt.................................................................. 3

3. Paraproct finger-shaped and thick, with banded color pattern; left paraproct longer than the right paraproct........ L. dewalti

-. Paraproct subtriangular, without banded pattern, subapically with creases; left paraproct smaller than the right paraproct.................................................................................................. L. crassus

4. Paraprocts weakly sclerotized, almost hyaline, laterally thickened.......................................... L. flata

-. Paraproct partially or completely sclerotized, not hyaline...................................................... 5

5. Paraproct subapically constricted to a needle-like spine................................................... L. acus

-. Paraproct without needle-like apical spine.................................................................. 6

6. Paraproct with an incurved apical hook, width almost equals the length............................... L. charliewattsi

-. Paraproct without an incurved apical hook, width usually shorter than the length................................... 7

7. Apical segment of maxillary palp elongated; RP of forewing with three branches; paraproct with concave inner margin and convex outer margin, apex obtuse with a small triangle.................................................. L. borisi

-. Apical segment of maxillary palp apparently shortened or subequal to basal segments; RP of forewing with two or four branches............................................................................................. 8

8. CuA of forewing with four branches; M partially fused with RP and CuA; apex of paraproct obtuse......... L. reni sp. nov.

-. CuA of forewing with three branches; M not fused with RP or CuA.............................................. 9

9. Apical segment of maxillary palp subequal; RP of forewing with two branches; paraproct strongly out-curved, with convex inner margin and concave outer margin, apex sharp..................................................... L. arcus

-. Apical segment of maxillary palp shortened; RP of forewing with four branches; paraproct points backward, apex blunt.............................................................................................. L. billwymani