Post 4. Potanthus omaha.
Note P. trachala have sharper wings & the upper spot of th HW band jutted out.

The veins are lightly darkened in P. omaha including those on the FW.
The FW spots especially spot 3 have slightly concave or straight outer margins.
The dark shading on the HW is very light.
Male on the left.
http://2.bp.blogspot.com/-SeSVvRKmjX...thus+omaha.jpg
http://1.bp.blogspot.com/-dKUEBsLc9P...thus+omaha.jpg

P. ganda is often confusingly similar.
Note veins on both wings barely darkened.
FW spots especially spot 3 have strongly concave margin.
Dark shading stronger.
Malaya.
http://m9.i.pbase.com/g9/25/686825/2...9.b3hmUCRI.jpg

TL Seow : Cheers.