What is this?

This piece of artwork was recently sold on eBay. It went for $1291.

The auction description read as follows:
>>>CARL BARKS - Original Artwork for Preliminary Paste-Up Drawing to Concept for the Cover to UNCLE SCROOGE No. 68, with Comic Book from HALL OF THE MERMAID QUEEN!- , FROM THE ESTATE COLLECTION OF CARL BARKS - circa March of 1967, Original drawings on velumn, pasted down to cover format paper, red-line and blue-line and lead pencil on paper and velumn. The background image with Scrooge is drawn on paper, the kids are on velumn, title and images are taped down, Image size is 12 1/2" x 10", unmatted. The comic is the reprint issue #125, which contains the same story. CONDITION is VERY GOOD with OFF-White paper.>>>

And here's the cover of US 68 that's referred to in the description:
Now, the regular blog reader will know that there's something fishy (pun intended) when I do a post like this. But you'll have to wait a while to get the answer. It's lunch time here in Sweden and Hedvig is bugging me about food. Got to do some shopping with her now, but I'll get back to this post later today or tomorrow.