Originally Posted by black
Yes Goosey, the second marbled shell looks like a Banded Wedge Shell Donax vittatus
. The seratted edge has a fancy name of marginal crenulations.
Staining of shells is quite interesting
Anaerobic bacteria living in anoxic sediments produce hydrogen sulphide that can interact with iron in the sediment producing iron sulphides that blacken sea shells. This blackening only usually occurs on the shell surface. If more oxidising conditions and iron is present - leading to the formation of ferric oxides then shells can be stained orange. Pink or red pigments can occur in some shells such as oysters depending on what the 'shell' was feeding on.
It looks as if Donax vittatusis could be prone to staining, I found another one yesterday which was stained. But that is a bit of a wild statement seeing as I have only ever come across two stained shells, not the sort of evidence to base a thesis on
The other shell in the image, also Donax vittatusis is void of all staining and very pretty, though it has been attacked, bored into by a Necklace Shell -Euspira catena and predated if the hole is full thickness (I didn't check