Short answer: I haven't a clue.
Long answer (my weak guesses

): Stomach contents...and it looks like there's a bunch of calcareous "stuff" in there (or at least it looks white and glisteny and jagged like calcareous fragments). I was under the (incorrect?) impression all ceph hard parts were chitinous except for cuttlebones and nautilus shells, so I'll say not ceph parts. But if it's not...then I'm not sure what it IS. I could swear that the items with the arrows look really familar, but...I just can't think what. And maybe these aren't actually hard parts at all.
Can I actually see a third "thing" that's similar to the other "arrowed things," directly above the top "thing?" If it is, well, those remind me most of some squid suckers...I think I've seen some with somewhat serrated edges near the inner rims as seen here.
But...I sure wouldn't bet money on any of that...so, mainly, I just haven't a clue! :?
This is fun!
rusty