Abstract
.Well-preserved early holaspid stages of the Cambrian Series 3 trilobites Ellipsocephalus hoffi (Schlotheim, 1823) and Ellipsocephalus polytomus Linnarsson, 1877 have been discovered in the Pibram-Jince Basin (Czech Republic) and Jamtland (Sweden), respectively. Both species show remarkable morphological changes during late ontogeny.
The earliest holaspides share long genal spines, and long macrospines on the second thoracic segment. Whereas macrospines disappear abruptly in later stages, genal spines are progressively shortened.
Consequently, the ontogeny of trilobites of Ellipsocephalidae is revised. The morphology of early meraspid cranidia and ontogenetic patterns in the disappearance of macrospines suggest that this family is closely related to members of Redlichiida rather than Ptychopariida.