phacops

from The Century Dictionary.

• noun A genus of trilo-bites typical of the proparian family Phacopidæ, with elliptical or oval carapaces, semicircular cephala with rounded genal angles, anterior lateral lobes fused with the frontal lobe to form a large swollen cranidium, and reduced posterior lateral lobes. The eyes are large, prominent, and schizochroal, the pleura rounded, and the pygidium semicircular with entire margin. The genus ranges from the Silurian to the Upper Devonian.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Paleon.) A genus of trilobites found in the Silurian and Devonian formations. Phacops bufo is one of the most common species.