Sk8r boi

Rachel Carson explains something that I often see on my infrequent visits to the ocean beaches:

The tidal flotsam abounds, too, in many little empty egg cases in which various sea creatures passed their first days of life…. The black “mermaid’s purses” belong to one of the skates. They are flat, horny rectangles, with two long, curling prongs or tendrils extending from each end. With these the parent skate attaches the packet containing a fertilized egg to seaweeds on some offshore bottom. After the young skate matures and hatches, its discarded cradle is often washed up on the beach.

—The Edge of the Sea, ch. III