Your ammonite probably is...
Lytoceras
Suture: Ammonitic
Lytoceras was from another advanced order of ammonites, but it was rather unusual in the fact that it had an evolute shell, meaning its coils did not actually touch. This is how it got its name, meaning "loose horn." It had large, well-spaced radial ribs with smaller radial ribs between them.
Courtesy Science Museum of Minnesota.
