Examples from the Web for undersurface
Until our families can come up from undersurface, it's going to be pretty lonesome, but we'll have to manage.
He pointed with his antennae to the fluorescent hieroglyphs on the undersurface of the saucer-ship.Clean Break|Roger Dee
The nest was some forty feet from the ground, on the undersurface of a shelf of rock.The Red Dust|Murray Leinster
The undersurface, originally a bright red, turns brown and runs in every direction into a mass of dark stalactites.The Life of the Fly|J. Henri Fabre
There had been a lot of that at first, in the early days before the transfer to undersurface was complete.