Giant trilobites and trilobite clusters from the Ordovician of Portugal Gutierrez-Marco, J. C. ; Sa, A. A. ; Garcia-Bellido, D. C. ; Rabano, I. ; Valerio, M. Abstract Publication: Geology Pub Date: May 2009 DOI: 10.1130/G25513A.1 Bibcode: 2009Geo....37..443G