Help ID What This Is

[Ed-D]

I've been carrying this around with me for years. I found it in north Texas; it looks like it has a repeatable pattern on the outside and some sort of inner core (best seen in photo #5) . I've done my best to get a photo from every aspect, plus some close ups. Any ideas would be appreciated.

Thanks!

 

[old digger]

What you have there is a section of an ammonite fossil.

 

[Ed-D]

Hey, how about that! Thanks. Now I can see if I can identify the type.