This is a beach/lounge cover-up from J.Crew that I'm calling the Ruffle Gauze Cover-Up (item #15544). It retails for $55, and is alpha-sized. It was available in a few different colors, including this one, SSE (I think soft seashell), and at least white as well. I can't remember if there were others. I tried this on in an extra small.
I think the cover-up runs a little on the bigger size, as I tried this on in an extra small, and it fit very comfortably. The small would have been pretty loose on me, and I think would have worked as well, since it is made to be a cover-up, and not a top. The material was a gauze-like material, and I would guess that it is a cotton gauze fabric. It is extremely light and breathable, which is always nice in a cover-up.
The cover-up has very generous armholes, and I would liken the sleeve shape to an extremely short dolman sleeve. It has a very deep V-neck, which is trimmed in ruffles, and has a tiny bit of shirring where the V comes to a point. Other than that, the cover-up has a fairly straight line, and looks almost like an oversized tee. I do wish that they had made the bottom flare out a little bit, rather than keeping it in a straight line, as it's a little tighter around the hips and thighs than the rest of the cover-up is in relation to the rest of the bottom. (Wearing your regular size would probably help here.)
I ended up leaving this one behind because I wasn't really in the market for a beach cover-up (because I hardly ever go to the beach, ahem ahem Boyfriend), plus I have a lot of old t-shirts that I could always wear. Plus I have a really cute gauze side-tie skirt from J.Crew a couple years ago that is a very cute cover-up.