Introduction: medium to large trilobites, typically surface sculpturing involves two size classes of granules or tubercles. 
Cephalon: opisthoparian sutures, glabella broad, extending to anterior border, with unique complex structure (lateral glabellar and occipital lobes often fused with each other and with cranidium). 
Thorax: 10-11 segments, pleurae initially horizontal, bend retrograde at fulcrum, end in free points.
Pygidium: large, usually flattened, often with 3 pleural pairs of leaflike or spinose structures.