Hi marinelife,
Looks more like an encrusting colony of
Hydnophora, given the darker, skeletal 'horns' (or
monticules) between retracted polyps.
Such corals have a dizzying repertoire of morphologies, from massive to branching. But the polyp arrangement around the monticules are nearly dead giveaways (indeed, the term for such a skeletal form is 'hydnophoroid').
Siderastreid corals aren't my strong suit, but if I recall correctly,
Psammocora is distinctly cerioid (the polyps in their corallite cups are cheek-to-cheek, so much that they each look polygonal in outline from above).
Nice purchase, BTW
Hydnophora can be pretty territorial, so give it space.
horge
