This species was first described by Edward Meyrick in 1885 using specimens collected in January at Arthur's Pass and named Mimaeseoptilis lithoxestus.

[5] In 1928 George Hudson discussing and illustrating this species in his 1928 publication The butterflies and moths of New Zealand using the name Stenoptilia lithoxesta.

[3] The male lectotype specimen, collected Arthur's Pass, is held at the Natural History Museum, London.

Forewings light fuscous, suffused with whitish-ochreous posteriorly and towards inner margin, and strewn with white in disc; a sharply-defined very narrow blackish-fuscous costal streak from base to apex, rather strongly dilated between 1⁄2 and 3⁄4, obscurely margined beneath with pale whitish-ochreous; a black dot in disc before and rather below cleft; apex and hindmargin rather darker fuscous, somewhat mixed with whitish; a fine black line along lower edge of first segment : cilia whitish-ochreous, on costa dark fuscous, within cleft and on hindmargin of first segment snow-white.

[5]Similar in appearance to Platyptilia charadrias but this species is larger in size, much neater in appearance, sharply defined costal streak, black line on lower margin of first segment, and absence of distinct dark line in cilia.