Key. Male adults of Sierracapnia species are separated by differences in (1) tergum 7 knobs, (2) epiproct proportions and curvatures, (3) epiproct membrane (or eversible crest), and (4) dorsolateral horns.
1 Epiproct linear in both dorsal and lateral view; shallow ventral keel (Figs. 13-15)............ palomar
1’ Epiproct thick in lateral view; deep ventral keel (Figs. 2, 6, 10, 18, 29, 36)....................................... 2
2 Tergum 7 knob narrow (10-15% segment width) (Figs. 3, 8, 37)..............................…....................... 3
2’ Tergum 7 knob wide (30-35% segment width) (Figs. 9, 17, 26) ……………................................... 5
3 Dorsolateral horns appressed to main epiproct body, membrane not visible below horns (lateral view); epiproct apex not raised; epiproct ventral keel less prominent (Fig. 6).......... hornigi
3’ Dorsolateral horns arch above main epiproct body and expose membrane laterally; epiproct apex raised; epiproct ventral keel prominent (Figs. 2, 36) …………………………………......... 4
4 Tergum 7 knob not notched and medium high (20-25% of tergum 7 height) (Figs. 2, 3); epiproct base with ventrolateral flange (Fig. 1); tips of dorsolateral horns extend forward to 70-78% of epiproct length (Fig. 2)............................... barberi
4’ Tergum 7 knob notched and tall (30-35% of tergum 7 height) (Figs. 34, 37); epiproct base lacks ventrolateral flange (Fig. 35); tips of dorsolateral horns extend forward to 85-88% of epiproct length (Fig. 34)........................... yosemite
5 Epiproct dorsal membrane light colored; epiproct apex narrow (dorsal view) (Figs. 9, 10) …………….…….............................................. mono
5’ Epiproct dorsal membrane dark gray or black (Figs. 22, 24); epiproct apex more broadly rounded (Fig. 28) ……………….......................... 6
6 Epiproct depth ≤20% length; epiproct reversely curved (lateral view); dorsolateral horns 14-18% epiproct length (Fig. 18); epiproct width uniform in apical third (Fig. 17) ………...………………………........…....... shepardi
6’ Epiproct depth>20% length; epiproct less reversely curved; dorsolateral horns 24-29% epiproct length (Fig. 29); epiproct width increases in apical third (Figs. 26, 28) …………………….............................. washoe sp. n.