Doug,
In the description he says "It has an open frame and 12 rectangular cups.
Each cup measures 2 1/2 x 1 7/8 x 3/4"." and "Jon Haussler lists this pan in his Muffin Pan Book as variation # 3 with a value of $700-900."
So my guess would be some sort of muffin or bread product.
If you are looking for more detailed explanation than that you'll need more of an expert than me.
Doug, 'gem' is an old-time description or nickname for a muffin. My grandfather called them 'gems' in his diner. And I have a couple cookbooks from women's groups in the midwest that were put together in the 50s that have recipes for 'gems'
They're just muffins...and my grampa's gems were round. But they could also be square, or round bottom/square top.