All genera previously referred to the Carcineretidae are herein evaluated, and the family is restricted to three genera, Carcineretes, Cancrixantho, and Mascaranada, for which diagnoses are provided. Ophthalmoplax and Longusorbis are herein removed to the Portunidae, and Longusorbis eutychius new species is described from the Eocene Tepetate Formation of Baja California Sur, Mexico, extending the range of that genus across the K/P boundary. The placement of Ophthalmoplax into the Portunidae marks the first confirmed notice of the family in Cretaceous rocks, a major range extension for the family. Important characteristics of the Portunoidea are discussed in the context of placement of fossil taxa within the superfamily and its constituent families.