ONTOGENY OF THE PROETOID TRILOBITE STENOBLEPHARUM, AND RELATIONSHIPS OF A NEW SPECIES FROM THE UPPER ORDOVICIAN OF ARGENTINA

Silicified material from the Early Caradoc part of the Las Aguaditas F ormation in San Juan Province, Argentina, includes a nearly complete g rowth series for a new species of the tropidocoryphid Stenoblepharum O wens, 1973. Cladistic analysis of Stenoblepharum species indicates tha t S. astinii new species is most closely allied to the Early Caradoc S . strasburgense (Cooper, 1953) from Virginia. Chinese species of Steno blepharum are sister group to a Baltic/Laurentian clade. A single adul t-like protaspid stage occurs in the life cycle of S. astinii, closely resembling the protaspis of Decoroproetus. It is preceded by a non-ad ult-like first protaspid instar that appears to be characteristic of P roetoidea in general but contrasts markedly with the early larval stag es of other taxa in Proetida.