What tort is this shell from?

[turtlewurx]

A friend of mine sent me this picture from San Antonio. She found it in a local shop & asked me to identify what sort of tort it was, since she didn't want to buy it if it was a protected species. I can't give her a definitive answer, & so thought I would ask here.

 

[Yvonne G]

That's a tough one. I depend a lot upon the actual tortoise when I'm making identifications. My first thought was a desert tortoise, but I don't think that's right.