We were rock-pooling this summer on the South cost of Brittany while the tide was out and I found this sticking out between some rocks. I dug it up out of curiosity and it felt like bone and had a hollow feel, as bone does when knocked. We had no way of taking it back with us at the time, and unfortunately it had gone upon returning, so luckily we had taken some photo's. The only point of reference of size I could find was my Blackberry, which is 4.2 inches long.
I would be really interested to know what it could be.