I've been pushing through Fate of Atlantis, and I am in the first ring of Atlantis. There is the lava machine, which requires a cup, which I have, and a stone fish head, which I do not. I've found two little inset shelves in the labyrinth. One of them had an eel statue, but the other was empty.

My understanding (and I've looked at a lot of walkthroughs) is that the empty shelf should have a Stone Fish Head for the lava machine. But in my version it simply isn't there, and it's not in my inventory. I don't have an alternate recent save I can go back to, so I think I might just be stuck if I can't find a necessary item.

Has anyone else experienced this?

The fish head you're looking for is on a small statue - you probably just missed it during your explorations. Take another circuit of Atlantis and make sure you've visited every accessible room!

Whoops, looks like you were right. It pays to look in EVERY room!