Acosmeryx anceus
Habitus: The smallest species of the genus. Wings not, or very faintly dentate. Forewing distinctly angled at vein M3. Palps, thorax underside and first two abdominal sternites paler than in other Acosmeryx species, more pinkish. Forewing upperside with oblique discal band diffused posteriorly; first discal line heavy, continuous; discal spot generally conspicuous; costal area greyish subapically, stopping at vein M1 or continuing beyond; a broad, curved, pinkish-grey submarginal line present, generally continuous with the apical lunules of the same colour. Underside of both wings different from all other Acosmeryx species. Forewing underside with a subapical, costal, triangular chestnut patch extending to vein M1, straight proximally, where it is bordered by a by a grey or pinkish-grey line or patch; outer part of discal area between veins M1 and 1A+2A not as dark as the subapical patch; submarginal area with extensive, diffuse pinkish-grey scaling; basal half of costal margin mostly of the same colour as the hindwing. Hindwing underside with brown marginal border vestigial, narrow, only reaching halfway to the second pair of discal lines at vein M2.
Male genitalia: Harpe notably different from the other species of Acosmeryx, being very elongate. Phallus with a broad left process, rounded at the tip, and dentate on the distal and proximal edges.
Female genitalia: Ostial plate notably different from the other species of Acosmeryx, the sides nearly parallel, suddenly converging apically, the apical part narrow, deeply concave; ostium covered by a half-cylinder, the apical edge of which is sinuate, with prominent, obliquely rounded lobes; proximal part of plate sub-membranous, almost regularly folded, the lateral parts smooth and deeply concave by the ostial half-cylinder.