Diagnosis. See the generic description for general facies features. This is a larger species than the next, with the wings a dark grey brown, the hindwings only slightly paler than the forewings rather than distinctly so, though this is variable. There are also differences in the course of the forewing postmedial as discussed under the next species.
Taxonomic note.N. externalis is treated as good species in Poole (1989). See also Owada (1987; 1994) and Lödl (1999e), who comments on the placement of cornicalis in Simplicia; the type material of cornicalis (ZMUC, Copenhagen) is placed more precisely in Simplicia on p. 113. Several additional synonyms are attributed to externalis by Poole (1989). N. cinerealis Walker stat. rev. occurs in Queensland, the Solomons and New Caledonia; it was illustrated as cornicalis by Holloway (1979). N. levicula Swinhoe stat. rev. is found in Sri Lanka and India and is a distinctly larger species than externalis with, in the male genitalia, slight bilateral asymmetry of a narrow, bifid valve apex and a spatulate saccular process that arises from half way along the ventral margin. The date of description of levicula as printed is 1889 (see also Poole, 1989), but a note on a reprint in the bound series (Tracts 2: 10) in BMNH indicates the paper was not published until 1890. The second Bornean species, cingala Moore, was also included as a synonym.
Geographical range. Oriental tropics to Sundaland, also China, Ryukyu Is.
Habitat preference. Chey (1994) recorded the species in abundance from softwood plantations and secondary forest at Brumas in the lowlands of Sabah, but it has not been taken in surveys of primary forest. Several specimens were collected by A.R. Wallace in Sarawak, probably in the lowlands, one being the holotype of indecisa.
Biology. Robinson et al. (2001) listed dry grass (including rice; Gramineae) and Dalbergia (Leguminosae) foliage as larval food.
