I just received a new shipment of matrix/prep material from the Wheeler Formation of Utah this afternoon. What should be looking at me from within the box is THIS! It is huge, about 3 inches wide by 5 inches long, very smooth and flat, with a well-defined margin to it. I don't yet know if I have the other side to it, yet.
First, I thought it might be the remains of a jelly, but I don't see any structures within, like concentric rings or radiating lines.
Then, I thought maybe it is a cephalon shield or carapace of a very large phyllocarid, like Branchiocaris. I am still feverishly researching every type of Phyllocarid it might be. There is only a very
faint area of changing width of slightly darker material, wrapping around the inside of the circumference of its margin/edge.
Did I finally get lucky?