A horn shark’s spiral egg case, found at Corona del Mar, California.
Photo: D.J. Eernisse, (c) 2002. From the NOAA website.
Here are some resources about “mermaid’s purses”—shark egg cases.
Some sharks hatch from egg cases, others are born alive from their mother. See pictures of shark births of all kinds over at SeaPics.
This U.K. website hosts egg case hunts in the United Kingdom. They have wonderful pages about how to identify an egg case, and crafts for parents and teachers and educators of all kinds.
Here is a shark egg case survey in Australia.