cornbrash bivalves id

Help please!

I found  these 3 bivalves in the lower cornbrash recently. The site is full of Pleuromya uniformis, but the first bivalve photo shows a much bigger specimen (refer to scale in cm) and ITS ONLY HALF of the specimen. It is double the usual size and particularly pointed out to the side. Half the specimen is missing (internal mould). Would this be another species of Pleuromya?

I am also sending 2 more photos of Pleuromya specimens. The second is also large and rather pointed. The final one is the usual Pleuromya uniformis size, with the valves open.

My question is are they all varying sizes of P. uniformis? Or separate types? (all from same site)

Thanks

and enjoy some cold hunting days out!!                       good luck Heath