A cap that is so rounded as to resemble half of an egg, or half of a sphere, is said to be hemispherical. Here, the emerging buttons on the right are hemispherical.
The terms ovate and ovoid are sometimes used in this sense.
An umbo is a softly curved bump in a flat cap. A cap with an umbo is said to be umbonate, as in the two larger mushrooms at the left. The two small mushrooms at the right have a central bump on a convexpileus, and are said to be campanulate, or bell-shaped. In this case, the bump is usually not considered a separate feature.
If the center of the cap is lower than the rest of it, the cap is said to be depressed. If the central depression is rather sudden and looks like a little hole, the cap is said to be umbillicate.
