Sorry to drag this old thing back up again..
also, the "under dress" appears to have some sort of lining on the bottom half because it looks a lot more opaque.. BUT it certainly isn't lined on the top. If you look at the pics they are a little......nipply? Suggesting that there is no satin dress underneath at all ^_^;; just a couple layers of the thin material with something opaque beneath the skirt for modesty reasons.
for the top layer.. the reason I call it the arm drape.. it looks to me like the front half of that is as you say.. a large half-circle that is attached at the collar and arms.