This is an uncommon Asaphus platyurus trilobite from the Vilpovitsy quarry near St. Petersburg, Russia. It's 3.75" long and nicely prepared from the surrounding limestone.
There are a few patches of shell restoration on the tail, but overall shell restoration is less than 5%
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.