Four trilobite specimens, two of Ordovician, one of Silurian, and one of Devonian age, display abnormal exoskeletal features ranging in expression from superficial to severe. Traumatic injury and developmental malfunction are considered the most probable causative mechanisms, each accounting for two of the abnormalities. Evidence of external healing of a marginal pygidial wound is apparent in one of the injured trilobites; the other may have succumbed to more extensive posterolateral pleural trauma. The two examples of developmental malfunction both involve disruption of axial and pleural regions of the pygidia. One was of limited effect, the second more severe and possibly fatal.