The Calymene trilobite dates to the Ordovician period (505 to 438 million years ago). These trilobites are common fossils from Morocco. Preserved with rusty-colored limonite crystals, these are actually the molds of the shells of Flexicalymene trilobites, and are often found in nodules, loose rocky concretions which reveal their fossil contents when broken open. Individual shapes and fossils vary but your item will resemble the pictured examples.