I know about as much about shells as I do about moths, so I have no idea what type it is. I think it came from Florida – the only time we went there we arrived just after a hurricane, and one result was that there were a lot of shells on the beaches. so I acquired several. This may be one of them – or not - I tend to pick them up whenever the opportunity presents itself!
It would be interesting to try to replicate this in hand dye and pin tucks.