Morphology and evolution of the eye in Upper Cambrian Olenidae (Trilobita)

The eyes of selected olenid species from Scandinavian concretionary shales were examined with the scanning electron microscope. Though these eyes are small, many previously unknown details were visible, including the 'peripheral zone' of Olenus wahlenbergi and other genera. Reconstructions, prepared by camera-lucida techniques, show the eye and the whole cephalon of certain species.In early olenids the visual surface was dehiscent in the adults and is preserved only in meraspids; in later genera the ocular suture became fused and the visual surface was retained. Details of lens distribution and manner of emplacement are described in Peltura minor, P. scarabaeoides, and Ctenopyge (Mesoctenopyge) similis. Evolutionary changes in the structure and shape of the eye are clear in different lines of descent. Some of the observed modifications are thought to be due to paedomorphosis. Some comments on the mode of life of olenids are also given