SE Texas - Hesperotestudo sp.?

[johnnyvaldez7.jv]

I found this 2 days ago on the 28th on a SE Texas river gravel bank. Beaumont Formation.

Size is 4.5 x 4 inches and 2.5 inches at it's thickest section and is heavy and solid. 

I believe it is from a large turtle and I think a Hesperotestudo sp. I'm not sure of where the placement might be and I haven't found a piece like this that has the flat smooth recessed area like a pad underneath it. I'm not familiar with turtles at all, but I was wondering if that was a giveaway to species and or location of this fragment.  

I'm sorry it's a lot of photos but maybe one of these might help someone later on with a smaller fragment. My apologies ahead. 

[Done Drillin]

If indeed from a turtle ( and please wait for more knowledgeable answers) it appears to resemble a piece of the plastron from the outermost edge. I have associated pieces of a specimen from the Peace River that bear a passing resemblance to yours.

[CDiggs]

I can't really speak to the position on the shell on a fragment this size but the texture of the cancelous tissue (spongy-bone) along the broken margins is classic Hesperotestudo.

The area circled in black is part of a suture where this segment interlocked with it's neighboring segment.