These characteristic egg cases of skates were common on the Atlantic side of the beach at the Chincoteague National Wildlife Refuge last month. I don't know which species they belong to. According to Lippson & Lippson (Life in the Chesapeake Bay, 2nd. ed., 1997), the clearnose skate (Raja eglanteria) is found near the south end of the Chesapeake Bay. Chincoteague is on the Atlantic coast and these egg cases may belong to the same species of skate and they indeed resemble the drawing of the egg case of the clearnose skate given at the link above.
The baby skates develop inside these cases (apparently one skate per case) and come out when they are ready to face the challenges of the outside world. I took one specimen that appeared intact.
This one didn't look like it was ever opened. So I was hoping to find tiny bones inside.
When I removed one side of it, there were these tiny rings, a few spine-like objects and some sand grains.
I don't know what those rings are. They are about 0.8 mm in diameter. Could they be skate vertebrae?