These are Trilobite Fossils in medium size. These have not been cut in two not polished so you can enjoy seeing the almost untouched outside. Note the range of sizes in the photo.
These are natural Moroccan variety. The photo shows the quality of those in stock. Some look as if there is re-glue as they are so frail. Note that the black ones with antennas on a white/grey base are usually concrete molds.
From Wikipedia: “The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period (521 million years ago), and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out. The last extant trilobites finally disappeared in the mass extinction at the end of the Permian about 252 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 300 million years.[6]… They have no known direct descendants. ”
We will intuit which is right for you and ensure that we choose a fossil in good condition i.e. not broken and re-glued. Photos and dimensions are indicative only as can vary a lot.