Devil's Purse

I found these on the beach when I went on photosafari and after asking around, one of my managers (Thank you Tim) told me he believed it to be the egg casing of a Skate, I googled it, and this is the description I got:
The skate is related to sharks and rays. It can range in size from one to three feet. Its flat body is white underneath, and its top colors vary from light brown to dark brown with black, roundish spots or bars. The skate is commonly found near shore in the summer, and you may see them riding the waves from the beach. Their skin is rough and prickly, but the thorny tail does not have a stinger like their ray cousins. It is called a Mermaid's Purse, or a Devil's Purse.