The ontogeny and dimorphism of Welleraspis lata Howell [in Cambrian Limeport Formation, Pennsylvania) is described. Statistically, 2 different minor features are characterized in the same genus and species, and these could reasonably be described as dimorphic phenomena. The immature forms can be separated into 5 developmental stages, as anaprotaspid, metaprotaspid, paraprotaspid, early meraspid and late meraspid periods. Beecher's term paraprotaspid period is adopted.

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