Need ID help for purple indo-pacific bivalves

[17saupe]

I'm having trouble identifying what species of (marine) oysters I have collected. There are two possible species I have considered and they are Dendostrea folium or Lopha cristagalli (perhaps I have found both) but I'm still uncertain and open to other possibilities. If someone could please help me with species identification that would be wonderful.

I found them in Perth, Western Australia: washed up under a rock and attached to rope and foam buoy.
The shells are externally a deep purple and internally a mottled white-yellow-brown + most specimens have an edge that is angular.
Thanks!!!