What you have there looks to me like a piece of flint or chert which comes in a variety of shapes and sizes and is often mistaken for fossils, however flint nodules such as this one often formed around organisms such as sponges which is what you may have here, if thats the case it would be from around around 70-100 million years ago towards the time of the end of the dinosaurs (late Cretaceous) which would fit with where it was found
yes i agree, its not bone, (athough i can see why you thought it was). it is definately flint.
aisling is correct about sponges, but i dont think that it is a sponge, it has the correct shape for a sponge, but it dosent have the correct structure (its smooth not rough). it might be a trace fossil where the flint filled in a borrow of a animal living on the sea bed.
bad luck this time, but keep looking... im sure you will find something!