It is shown in either the RB or BB, but I don't recall what it says about it. The pattern is taken from a Griswold #2700 wheat stick pan, but Griswold gem pans only have hanging holes in one handle. Griswold also made them marked #1270 Best Made S.R and Co. Whoever made it, they knew what they were doing, casting-wise. A Wagner "B" pan is an 11-cup popover pan.
Related:
http://www.castironcollector.com/gems.php