Tri-Lobed: The name trilobite was given to these creatures because their exoskeletons are divided into three distinct lobes, or parts. The soft parts and the legs on the lower surface of the animal were very seldom preserved. Whole fossil trilobites are surprisingly rare, but they can be found in rocks from the Cambrian to the Permian Period (about 590 to 250 million years old). They became extinct after that.
This one is about 120 mm long.