Cowboy,
Thats an american snapping turtle. I fish for em around here during the summer (ol summer time kick back from growing up in Louisiana) Unlike Jerrys streaked head turtle shell you just can't clean out a snappers shell and it be OK.
They're shells are sort of like a gators skull. Lotsa pieces jammed together like a jigsaw puzzle. Only thing is there's alot of cartilage and even some muscle fibers running through and beneath the scales that make up a turtle shell.
In other words......... a snappers shell will fall to pieces and need to be reglued back together.
I think there's some sort of professional method in curing them that keeps this from happening. But everyone I've ever boiled (takes a BIG POT!) or cleaned and left out to dry, has just fell to pieces.
BTW thats some extremely delicate and good eatin you got there as well.