There is a row of dots along the rim at the front of the head, just before the glabella (see detail of head). Are those dots bumps or pits? The third photograph answers this question. It is taken with light coming only from the right. The trilobite lies in a shallow pit created by the preparator; the side of that pit is dark because it is in shadow. You can see the line of dots just before the glabella -- if they were bumps they'd be lit up and would be light in color, but they are dark and in shadow so they are pits.

What were the pits for? My guess is that they had a sensory function. In life they may have had small hairs that served to detect vibrations and sound.