The officially published lyric in the gatefold of The Wall is:
“With your nerves in tatters as the cockleshell shatters…”
So the correct word is cockleshell.
The song itself, of course, is Run Like Hell, written by Roger Waters and David Gilmour.
“Cockleshell” is an old English word for a small shell (from the cockle), and it also carries a nursery-rhyme echo — “Mary, Mary, quite contrary… silver bells and cockle shells…” That faintly archaic, sing-song quality fits the album’s recurring strategy: innocent or nursery imagery warped into menace. The line isn’t a Lord of the Flies allusion; it’s more in keeping with the brittle, almost childlike imagery scattered throughout The Wall.
As for pronunciation, “cockleshell” is straightforwardly pronounced “COCK-ul-shell.” If someone hears “conch shell,” that’s likely just a case of live diction plus Waters’ tendency to compress syllables under stress. But textually, it’s not “conch,” whether pronounced “contch” or “conk.”
So: no Greek etymology puzzle, no Golding reference — just a shattered cockleshell.