This one has me pretty confused. My initial thought was that it was a nautiloid, but upon closer inspection, I realized that I did not see any sign of chambers, which made me question that ID, so maybe it's a gastropod? I'm not sure how clear this is from the photos, but the spirals are continuous (e.g., they are not stacked disks as I've seen in some nautiloids). Any thoughts here would be very much appreciated. Sadly, I did not find this specimen myself, and so I do not have any particularly useful information on age or location. It was left in a desk drawer along with a collection of other invertebrate fossils, most (if not all) of which are Paleozoic in age. Here are the pictures. Thank you in advance for your time and input.