Found this on a beach in the States (Washington State, Puget Sound). Looks like a skull of some sort as there seem to be eye sockets. I could be totally wrong though. It's also quite rubbery so I believe it's cartilage. The closest I could find was this post on flickr:
Being rubbery would indicate cartilage and the appearance is very much like a shark/ray/skate cranium (brain case). I have never seen a sawfish cranium but it is certainly a shark with a long snout, you could search guitar shark as well.