The pileus is often umbonate or gibbous, and the center is often darker than the margin.
"Studies of American Fungi. Mushrooms, Edible, Poisonous, etc."
George Francis Atkinson
At the other gibbous horn of this Athens of the Athabasca rise the steeples and convent-school of the Roman Church, with the free-trading-post of Colin Fraser.
"The New North"
Agnes Deans Cameron
About an hour before midnight the two moons passed each other in the Eastern sky; both gibbous at the moment, like our Moon in her last quarter.
"Across the Zodiac"
Percy Greg