This is an excellently prepared specimen of Zlichovaspis rugosa quarried from Atchana, Morocco. At 3.5" in length it's a large trilobite and it has been prepared so that it displays very aesthetically on a base of limestone. Much of the matrix has been removed from underneath it, and the hypostome (mouthplate) is visible. Great detail and eye facets with no restoration work. Really a spectacular trilobite.
 
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).