Meanings of open cover in English

From the open cover, a round watchpaper feathered out and settled on his knee, face down.

By keeping just in their rear we might be able to urge them gently along until they should enter more open cover.

I am always careful to open covers cautiously, and to preserve seals entire.

One seldom halted long enough to open covering-fire, and besides, there was nothing to fire at.

The train consists of two engines, two open covered carriages for the second class passengers, who are mostly natives, a saloon and baggage wagon.