PHACOPS

genus of trilobites (an extinct group of aquatic arthropods) found as fossils in Silurian and Devonian rocks (between 345,000,000 and 430,000,000 years old) in Europe and North America. Phacops is a common and easily recognizable form, with its rounded rather than angular outline, globose head region, and large compound eyes. A common form is the species Phacops rana.