A well preserved tiny fossil trilobite! Trilobites are extinct marine arthropods but before they all died out around 251 million years ago, there were many different species around the world. This one is a phacops megalomanicus from the Atlas Mountains in Morocco.
This species and many others had raised compound eyes providing excellent vision, and you can still see them on this specimen. Just amazing preservation!
Some species could curl up; displaying them tail down like this is the accepted way to mount such fossils. The base is polished stone.
1/2 inch (1.3 cm) wide, 7/16 inch (1.1 cm) deep and 1/2 inch (1.3 cm) tall.