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A medium-size pale grey moth with a dark band and lines crossing the forewing. Very similar to and often mixed in collections with Furcula scolopendrina and F. modesta. The light areas of the forewing are pale pearl grey in occidentalis (white in scolopendrina and pale tan in modesta), and the series of fine, parallel zig-zag lines crossing the outer half of the forewing are sharper and more complete in occidentalis, but usually blurred or incomplete in scolopendrina. Specimens from the foothills and mountains may have to be dissected for positive determination. The male of occidentalis has a much shorter, stouter tip to the uncus than scolopendrina does. Both sexes are similar, but the females are larger and broader-winged, and with filiform antennae (bipectinate in males). Specimens from the mountains are larger and darker, and have been named subspecies gigans.