This is a bargain Hollardops merocristata trilobite quarried near Issoumour, Morocco. It shows quite a bit of surface detail including preserved eye facets. The preparation is pretty rough in areas leaving surface scratches on the shell, hence the bargain price.
Trilobites were a very diverse group of extinct marine arthropods. They first appeared in the fossil record in the Early Cambrian (521 million years ago) and went extinct during the Permian mass extinction (250 million years ago). They were one of the most successful of the early animals on our planet with over 25k described species, filling nearly every evolutionary niche. Due in large part to a hard exoskeleton (shell), they left a excellent fossil record.