They have a single large black horn in the middle of the forehead...

The summer male has black "horns", which give this species its American name.

They have a small fleshy black "horn" above their eyes.

Thin black horns punctuated the top of their long faces.

The first instar is pale green with a black horn.

Look for a green banner with a black horn upon it.

On the tail, they have an entirely black curved horn.

She flew toward impalement on their black horns of death.

It has a very long, black horn on the end of the abdomen.

His large head was protected by massive long black horns, six feet across, that curved out and then up.