The pileus is rounded, then convex, becoming nearly expanded and sometimes with an umbo.
It is by the position of the umbo in the grave that this fact has been exactly ascertained.
The summit or apex of the valve is called the umbo, or beak.
The heel or umbo is either angular and prominent, or rounded.
umbonate, bossed; furnished with a low, rounded projection like a boss (umbo).
They are sometimes bell-shaped and then flattened, often with a mound or umbo.
The centre was formed of metal, and was called a boss or umbo.
umbo Stetson, Orne's section chief, went back into his cruiser's "office" after a hospital flitter took pod and patient.
umbonata, having an umbo or conical projection like the boss of a shield.
umbo: The beak of a bivalve shell; the protuberance of each valve above the hinge.
1921, from Latin umbo "shield-boss, knob, projection."
umbo um·bo (ŭm'bō)
n. pl. um·bos or um·bo·nes (ŭm-bō'nēz)
A small anatomical projection on a surface, such as that on the inner surface of the tympanic membrane at the end of the manubrium of the malleus, corresponding to the most depressed point of the membrane.