Ordovician Period   Origin of the Term Ordovician System. [1879] Charles Lapworth established the Ordovician from studies in Wales and elsewhere based on distinctive graptolite fossils. By this time trilobites were known from rocks below classical Silurian (in Sedgwick's Cambrian); the corals of the Silurian were different from those found in this new system. Lapworth made a complete sweep of the Lower Paleozoic; he redefined Murchison's Silurian (became more restricted and precise), created a new system, and reinstated Sedgwick's Cambrian System, but defined it on the basis of distinctive fossils (in particular, trilobites). Stanley M. Awramik