Moygashel vintage Irish linen floral cut out lace sheath dress size M

Vintage 1960s? fine Irish linen floral lace lined dress. I would call it Oatmeal in color with a cream color satiny lining. Long inv metal zip closure in back. The only tag is the Manufacturer....no size or care tag. The measurements are laid flat 17 " pit to pit. 15" waist. 37" long. The armhole openings seem quite small they measure 5.5" flat. It seems to be in excellent vintage condition. The lace intact. One small spot on the upper back. I didn't try removing it, see last photo