I've seen your pics of these before; they're cool for different reasons. The one in the first 2 pics would be nice to see in some close-ups. It looks like most of the detail is worn off, but it could go a couple of ways on the ID. That it came from a midden is interesting.
The one in the last 4 pics has great detail. If it has 5 small "pin-holes" almost in the center, then it is most likely Coenholectypus planatus.