This is a natural double Arctinurus specimen from the famous Caleb Quarry near Middleport, New York. Very few multiples of this rare, Silurian lichid trilobite have been found over the years. Both specimens on this plate of over 5" long which is quite large for the species. There is minimal restoration, mostly on the pleural spines of the specimens.
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.