Need Help With ID Of Fresh Water Fossil.

[Nigel Tufnel]

First things first, I am quite a neophyte to the world of fossils.

I found this large shell while kayaking the San Marcos River. I regularly hunt Indian artifacts and I think this one appears to have some type of flint in the outer-most layer.

It is VERY brittle. It also has what appears to be "fossilized" sand in the deepest recess.

If anyone could shed some light on this one for me I would be in your eternal debt! I always find shells while kayaking but never one this large and colorful.

Thank you for any help in advance.

 

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[Harry Pristis]

It's a marine fossil, Cretaceous in age. It's one valve of Exogyra sp.

 

[Nigel Tufnel]

It's a marine fossil, Cretaceous in age. It's one valve of Exogyra sp.

Thank you very, very much for your help.