Plectophila placocosma is a moth in the family Xyloryctidae.

The forewings are white, slightly ochreous tinged and with a broad dark fuscous fascia suffused on the lower half, the anterior edge curved from one-sixth of the costa to one-sixth the inner margin.

There is a large irregular fuscous patch on the costa beyond the middle, reaching more than half across the wing, the anterior edge preceded by a blackish discal spot.

There is a large fuscous patch on the hind margin from the apex to the anal angle and a fuscous hindmarginal line, separated from the preceding patch by a streak of the ground colour.

The hindwings are yellowish, with a broad fuscous suffusion occupying the posterior two-thirds of the wing.