Key to species of Nenasa

1 Male forewing with an oblique pale yellow stripe from its base to the middle (CHAN & YANG 1994: fig. 4D). Rostrum with third segment longer than wide. Hind margins of male pygofer concave (CHAN & YANG 1994: Fig. 4E). Phallobase narrow (CHAN & YANG 1994: Figs 4G, H). Male anal tube, in dorsal view, elongate, narrowing apically, without apical concavity (CHAN & YANG 1994: fig. 4F). Taiwan. ...... .................................. N. obliqua Chan & Yang, 1994

– Male forewing with a large light yellow spot basally and a light yellow inner margin (Figs 1, 2). Rostrum with third segment as long as wide (Fig. 11). Hind margins of male pygofer straight in lower two thirds, convex in upper third (Fig. 18). Phallobase wide (Figs 15–17). Male anal tube, in dorsal view, wide, almost rounded, with weak apical concavity (Fig. 22). Fujian. ........................................... N. ouchii sp. nov.