These are fragments of pleasiosaur ribs with some gastroliths in the rock surrounding them (top right hand side). Gastroliths are stones swallowed by plesiosaurs to act as ballast to help them balance and to enable them dive down in the water. Modern crocodiles use gastroliths like this too.
The specimen is unprepared, meaning it has not yet been cleaned. It can take a huge amount of time to remove the rock to uncover the bone. Most of the spectacular fossil skeletons of marine reptiles and even dinosaurs start off like this. A piece like this could take over 100 hours to prepare.
Find out more on the reptiles pages.