This species was described by Edward Meyrick in 1914 using material collected at Ben Lomond in November by Alfred Philpott.

Forewings triangular, termen bowed, rather oblique; black; six ochreous-white transverse lines, first cloudy, ill defined, second and third nearly straight, third rather thick, fourth fine, angulated in disc, fifth thick, rather curved outwards in disc, sixth slender, curved, very near termen on lower half; a transverse ochreous-white mark in disc between third and fourth: cilia white barred with dark grey.

Hindwings with termen rounded; blackish; basal area irrorated with white; three ochreous-white transverse streaks, first before middle, narrow, somewhat angulated in disc, with a distinct prominence from angle, second at 2⁄3, rather broad, bent in disc, third narrow, rather waved, curved, prae-terminal: cilia whitish, barred with dark grey on basal half, and with extreme base irregularly dark fuscous.[3]N.

[4] N. hexaleuca also has visually different curved or straight lines on its forewings giving it a lighter appearance than N.

[9][1] Other than the type locality of Ben Lomond, N. hexaleuca has also been found at Flagstaff hill in Dunedin, at Mount Cook, at Skelmorlie Peak near Lake Te Anau, at Cluden Station near Tarras, in the Kakanui Mountains and at Mount Herbert.