Abstract
Summary: Cyclopyge genatentaStubblefield, 1927, is interpreted from new material, and established as the type species of a new cyclopygid genus,Prospectatrix. The morphology ofProspectatrixshows that the cyclopygids and nileids are closely related, and together with the Taihungshaniidae, these families are included in an expanded concept of the Cyclopygacea. The subfamily Ellipsotaphrinae Kobayashi and Hamada, 1971 is excluded from the Cyclopygidae. Pelagic habits arose on at least five separate evolutionary lines among Ordovician trilobites:Prospectatrixlies near the origin of one of these.CremastoglottosWhittard was derived from a robergioid ancestor by forward migration of the eyes.

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