I found this on a beach in Jersey this Summer, and was wondering if anyone could identify it? It's about 3.5cm wide.
This is/are the pharyngeal teeth of a fish (ie at back of the throat). As far as I know most likely a wrasse.
see eg http://www.agefotostock.com/en/Stock-Images/Rights-Managed/FHR-33140-00005-840 , http://www.nhm.ac.uk/natureplus/message/7576 , & http://www.glaucus.org.uk/Torpedo2013Jan.htm (& scroll down the page)
In fact, comparing your clear pictures with the stock photo it's a virtually perfect match (& Steve Trewelha is a top uk shorelife photographer), so it's pharyngeal teeth of a Ballan Wrasse.
I'd be interested to know if you marked this question as 'assumed answered' ? (the alternative is that a member of staff did & would be unusual). I'm interested as you've only had my answer as yet, & one consequence is that your question now has the same symbol on the list as those on the list that are marked as 'answered', so there's much less chance of members seeing it & providing a better answer or better proof. It also greatly decreases the chance of the museum ID team looking at it,as they only get email alerts for questions still marked 'not answered'. Also the 'assumed answered' option can't be undone as Ellie Comley found in http://www.nhm.ac.uk/natureplus/message/36514 ( though you can still mark an answer as helpful (& even mark 2 answers as helpful) or mark an answer correct) whilst marking as 'helpful' or 'correct' can both be undone.
A 3rd remarkable property of 'assumed answered' is that while it might be taken as an indication an answer is probably correct that is only temporary,ie any question older than about 5 months is marked as 'assumed answered', even if nobody's answered at all. So eg in bottom 3rd of P.1 of the 'all animal life' list ( http://www.nhm.ac.uk/natureplus/community/identification/all-animal-life?view=all#/?per_page=50 ) is a chrysomelidae question http://www.nhm.ac.uk/natureplus/thread/10166 ,with no answer yet assumed answered & there are no 'not answered' questions in the 3 & a bit pages before despite 5 having had no reply. The same is true in the other lists.
There's also a clear picture of it in the RSPB book of the seashore by Maya Plass P.226 as the Bollan cross, "worn by seafarers as a talisman"..."pharyngeal teeth of Ballan Wrasse"..."Similar species None"