Is this a bone by chance? This one I am positive came from theMissouri side of the Mississippi river bank!

[TinySpiderMonkeyNinja]

I did find this item on the river bank of the Mississippi river, in a tiny cove right smack between Alton, IL and St. Louis county, MO. No digging required, I was just trolling the embankment. Do you think it is bone? All the photos are the same item, just different angles and close ups. 

[Lone Hunter]

No it's not bone, not sure what kind of rock but I think I see some inclusions that may be fossil.

[Tidgy's Dad]

I think it's limestone.