Petalism

Witnesse the Ostracisme amongst the Athenians, and the Petalisme among the Siracusans.

They've identified a reference to the ancient Syracusian practice of banishment known as petalism, and what may or may not be a reference to efilism, a branch of the antinatalist philosophical position advanced by Schopenhauer, but what any of that has to do with the lyrics' subsequent allusions to Moby-Dick seems pretty open to question.