 The world's largest-known trilobite specimen, assigned to "Isotelus rex" of 72 cm, was found in 1998 by Canadian scientists in Ordovician rocks on the shores of Hudson Bay.The exoskeleton is composed of calcite and calcium phosphate minerals in a lattice of chitin that covers the upper surface (dorsal) of the trilobite and curled round the lower edge to produce a small fringe called the "doublure".Three distinctive "tagmata" (sections) are present