Potamyia, like Cheumatopsyche, have a small or inconspicuous pair of sclerites under the prosternal plate that are difficult to see. Contrast that with the larger pair of sclerites found on Ceratopsyche. To access sclerites, it's best to gently pull the pronotum and mesonotum in opposite directions. Note: the large single sclerite is the prosternal plate. Posterior margins of sclerites on abdominal sternum 9 are entire (there are no notches).
The foretrochantin may or may not be forked, and there is a prominent anteriomedian projection on the anterial ventral apotome of the head.