Similar species: Polyptychus sonantis (Jordan, 1930).
Even though it seems to be difficult to distinguish sonantis from trilineatus on habitus, we have observed a character on the forewing pattern that seems to work most of the time in our specimens. The most distal dark post-medial line is gently convex, between M3 and CuA2 in P. trilineatus (Fig. 1.6b), while it is prominent on veins M3 and CuA2 and convex between these two veins in P. sonantis (Fig. 1.6a). This character is particularly useful in the field for separating P. trilineatus from P. sonantis, given the two species coexist in southwestern India.