An Ancient

When this was first described to me I thought it was an ammonite. After this phone pic was sent to me I'm not so sure. It is a complete specimen but doesn't join like an ammonite and looks a little like it has a head and tail. My son said he can see little scales when he looks closely. Some kind of fish without fins? A sea slug? I'm going to have to do some investigating on the Internet and see if I can find out what it might be or might have been. Texas has so much limestone and lots of these sea creatures everywhere you look. I have a few ammonites found when digging the foundation of my house and the kids have found trilobyte looking things and a piece that looks very much like a razor clam near here. This piece is a mystery to me. It is approximately 16" in diameter and about 4 to 5 inches thick. I haven't seen the bottom, I wonder if it had legs? Well, anyway it will be at my house sometime this week and I'll get a good look.