I notice you have two posts on a similar theme. This photograph is of the thoracic sternum of a crab - this is the very underside of the crab, less its legs and abdomen/tail. Difficult to identify exactly which species but possibly the edible crab, Cancer pagurus.
What can be said about it though is that it is from a female, or hen crab. The two circular holes were the genital openings. In life these would be covered by a wide abdomen, such as the one in the photo in your other post.
It does not seem impossible that both parts are from the same crab - at least same sex, and possibly same species.