Big Shell

Back when I was in high school, the district built a brand new auditorium. The roof was shaped like a giant sea shell. What's the name of those shells that spread out like a fan?
That high school isn't far from LAX. Planes, taking off, swooped first over the Pacific Ocean so that if they crashed during take-off the heavily populated land below would not have human life and property smashed to smithereens. This was a needless precaution really. Planes don't crash much. But the safety route does afford passengers a wonderful view of Balboa's Pacific. If they know where to look, they can also see the gigantic seashell roof of my high school's auditorium.