I have never found complete Trilobytes. Only parts of them. The part I found in the Ardennes is the back part of a Trilobyte I couldn't find on that page.
If you want to learn more about Trilobytes, try this excellent page :
This site was once a border between France & Belgium. I don't know what 's the word in English, but I call it a "checkpoint" now. As I was there, it was already prohibited to collect there. It's still very popular, apart from the fact that it isn't allowed to collect there anymore.