The occurrence in the Arenig of the Oslo Region of the typically east Baltic trilobite Megistaspis (Rhinoferus) hyorrhina (Leuchtenberg, 1843) is confirmed. The Norwegian specimens exhibit a range of variation just as wide as that seen in the east Baltic. The visual field is estimated and found to overlap posteriorly and 20° above horizontal. The glabellar tubercle in asaphids is considered to have functioned as a pressure-sensitive organ. The swelling of the posterior part of the glabella in some specimens, may have been to lift this organ as high as possible. This interpretation, together with the elevated eyes and the flattened exoskeleton, suggest a shallow infaunal life habit.
The Lower Ordovician trilobite Megistaspis (Rhinoferus) hyorrhina (Leuchtenberg, 1843) (Trilobita) in Norway, with notes on its autecology