The a7R is not compatible with the Nikon 24mm f/3.5 ED PC-E Nikkor with any adapter that I’ve tried. The “E” in the name stands for electronic diaphragm, and I know of no adapter that supports it. If there aren’t any adapters that support the lens, that’s too bad, because the PC Nikkors seem otherwise like they’d be a good match for the a7R, which offers much nicer live view focusing than the D800E.
Thanks to Nick for pointing this out. He says it’s true for the other newish perspective control Nikkors: the 45mm and the 85mm.