Fossil found at Bailly, France

I found this unusual fossil in a piece of limestone in a road cutting in Bailly, France, in 2002.

The only suggestions I have had is that it is a section from something like an ammonite. However the very unusual internal structure appears to be a continuous clockwise spiral. I have not been able to find any reference to any similar structure on the Web.

 © Roger Riordan 2004-2017

Unusual fossil found at Bailly, France