It’s the goniatid—or if you prefer the goniatite—Imitoceras rotatorium, and what’s not to love? Stephanie Keep recently told you about the collective NCSE fondness for cephalopods, and goniatites are cephalopods found in the fossil record from the Devonian to the end of the Permian; they resemble their later cousins the ammonites.
There was no correct answer submitted, perhaps owing to the now-fixed problem with the comments. (Was the reference to a scanning superconducting quantum interference device—or SQUID—a help or a hindrance?) At least I can offer a tip of the crinoid-holdfast-adorned hat to Dan Phelps and his celebrated wheat penny for the photograph of the fossil.
But I also have to award one (1) internet to Steve Bowden, who, even despite the problem with the comments, followed the instructions diligently in submitting his answer: