TOTALLY a cute 70s-does-30s number! Even more so with my version! The picture on the envelope is kinda hippie-ish. Mine just looks like a short 1937 house dress! I followed the directions and pattern exactly -- even the pockets and buttons, which I usually free-hand. The result was perfection! I should follow the pattern more often! Nothing about the pattern was too difficult and it's good for advanced beginner/low intermediate (me) sewers.
And let's talk about BUTTERICK not putting copyrights on their patterns well into the 80s. Obviously, we can all see this is a 1970s pattern. The blonde on the envelope has the same haircut as an actress on a 1973 episode of The Brady Bunch I saw the other day so there's a clue. Another is my handy-dandy Sears pages. It seems like that cut and collar is on every other page of the 1974 catalog, so I'm dating this pattern to ca. 1974. Here's the "proof":
All pages with dresses very similar to Butterick 3138! And all so CUTE!!