The last of the fossils that was given to me by my friend Don, during a visit last fall, are these Dakoticancer australis crab fossils. He found these in the Coon Creek formation near Blue Springs, Mississippi.
This first one was preserved by Calcite and is pretty much just the upper and lower body carapace.
This second specimen is more complete and I think is preserved by phosphates rather than Calcite.
The Coon Creek formation is dated to the lower Masstrichtian stage of the upper Cretaceous.
I found this paper on the FOSSIL DECAPOD CRUSTACEA FROM THE LATE CRETACEOUS
COON CREEK FORMATION, UNION COUNTY, MISSISSIPPI.
And here is one on the Coon Creek formation paleoenvironment and depostion.