This fossil is an asaphid trilobite or related, a broad-bodied, smooth-shelled kind of trilobite common in Ordovician seas. Its wide oval shape, large head shield, segmented middle, and rounded tail fit that general look better than the spiny or big-eyed trilobites many people know from later periods. That would place it roughly around 470 to 445 million years ago, when shallow seas were full of armored arthropods like this one. I would stay cautious about naming an exact species from the photos alone, but calling it an Ordovician asaphid trilobite is a solid, reasonable label.