Oh, COOL! Since my muddy had a beautifully speckled head and neck, then she was a hippocrepis!Looks like an eastern mud turtle to me. Kinosternon subrubrum subrubrum
With the first vertebral seam quite separated from the second marginal it has to be a K subrubrum. The Yellow Mud (Kinosternon flavescens) has that seam in contact with the second marginal.
Subspecies wise - The eastern (K s subrubrum) can be more plain looking while the Mississippi (K s hippocrepis) tends to be more speckled on the face and neck.