Twentyfour nearly complete carapace samples were collected at three different localities of the Maastrichtian (Late Cretaceous) Cardenas Formation in San Luis Potosi, eastcentral Mexico. The material has been assigned to five families: the Callianassidae, Dakoticancridae, Carcineretidae, ?Majidae, and Retroplumidae. Two genera of callianassid shrimp are described, Cheramus for the first time in the fossil record. Dakoticancer australis Rathbun is reported as the most abundant crustacean element
one new genus and species of carcineretid crab, Branchiocarcinus cornatus, is erected, and a single, freagmentary specimen is questionably referred to the Majidae. The three localities reflect paleoenvironmental differences, exhibited by different lithologies, within marginal marine, lagoon environments. The record of dakoticancrid crabs in the Cardenas Formation extends the paleobiogeographic range of the family and the genus Dakoticancer. Carcineretid crabs, although not abundant, seem to have been a persistent element of crustacean assemblages in elastic environments during the Late Cretaceous of the ancestral Gulf Coast of Mexico.
