Sentence:  Head, thorax, and abdomen yellow and white. Fore wing white, with the costal half to end of cell suffused with fuscous; an obscure fuscous triangular <WSD>postmedial</WSD> mark with its apex on inner margin, its inner limb with a black speck ... 
Meaning of the word marked with <WSD> tags:  Located behind (further towards the rear than) the middle.