Abstract
Summary: The three species of Placoparia; P. (Placoparia) cambriensis Hicks, P. (Coplacoparia) tournemini (Rouault) and P. (Coplacoparia) borni Hammann have been recognized from the Ordovician of North Portugal. New subspecies of P. (Placoparia) cambriensis have been established on the basis of differences in the pygidium and suggests the presence of two, broadly coeval, populations in western Europe during the Llanvirn. Quantitative analyses have provided information on growth patterns.