Found Art

This piece of 'found' art is known as 'Cu Chullain's Shield'. Can anyone guess what it really is?

My Uncle, now a man in his eighties, who did not recognise me when I visited him recently, gave me this piece of art from his collection of 'found' art. The items are bits and pieces that he picked up, mostly on sea shores, and put together, without altering them in any way. Many of his pieces are beautifully smoothed and refined by the sea and sand.

In mythical Ireland, Cu Chullain was born Setanta until he killed the hound (Cu) of Culann and pledged to guard Culann's Castle until Culann found another equally loyal hound.

In reality, the actual piece is very far away from the era of Cu Chulainn.