Joe,
I tie this version for Baetis/BWO's. Just change out the colors for a PMD...
SPLIT WING CASE BAETIS NYMPH
HOOK: Daiichi 1130, #16-#22, TMC 2487, Mustad C49S
THREAD: Gordon Griffith 14/0 Sheer, Olive or Gray
TAIL: Lemon Wood Duck
ABDOMEN: Goose Biot, BWO, Olive or Natural
RIB: Lagartun Gold x-fine wire
THORAX: Wapsi Beaver Dubbing, Dark Tan
LEGS: Lemon Wood Duck
UNDER WING CASE: Wapsi Razor Foam,Translucent Dun, 1mm
OVER WING CASE: Spirit River, Black Holographic Mylar Motion 1/64", 3 strands each side, tied at sides and pulled over the foam...this is tricky, patience prevails. One can also touch up the wing case with a dab of UV resin (Silver Creek offers a good one)
HERE is another,interesting version from Greg Vinci (C & P):
http://www.flyfisherman.com/west/california/californias-truckee-river/
PT/TB