This is bizarre trilobite looks like something you might see in an Alien's movie. It's fittingly name Dicranurus monstrosus. While fakes of this trilobite abound, real examples like this one are fairly rare.
This one is real and measures 3.3" wide, spine tip to spine tip. There is a bit of disarticulation to the body and a natural seem running through the trilobite. There is some restoration along repaired cracks, with most being on the first few segments on the left hand side of the body, maybe 3-4% in total.
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.