This is a beautiful, 1.4" long, prone example of a rare Ordovician trilobite from the Putilovo Quarry. It's a Niobella lindstroemi, with very nice preservation. There is only some very minor restoration on two pleural tips on the right hand side.
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.