The protaspides of Missisquoia depressa (Missisquoiidae, Trilobita), from the uppermost Cambrian part of the Rabbitkettle Formation, Mackenzie Mountains, northwestern Canada, are described. Three metaprotaspid stages are recognized, using size as well as features of the anterior border of the cranidium and the shape of the glabella. The morphology of the protaspides is not typical of the Order Corynexochida, suggesting that Missisquoia is not a member of the order to which the genus has been previously assigned. This further indicates that its affinity to the stratigraphically younger styginids and illaenids is questionable.

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