Five new species of mollusks are described from the early Eocene Maniobra Formation, northeastern Orocopia Mountains, southern California. The new species are from the basal part of the formation, and the fauna is indicative of the West Coast provincial molluscan early Eocene “Capay Stage.” The mollusks are shallow-marine forms that were transported a short distance into slope/upper submarine-canyon deposits.
Chedevillia saltonensis n. sp. and Eocypraea? maniobraensis n. sp. resemble Eocene species from Paris Basin, France. Phalium (Semicassis) louella n. sp. is the earliest North American species of Semicassis. Volutilithes orocopiaensis n. sp. is the earliest North American species of this genus and resembles V. muricinus from Paris Basin. Glossus (Meiocardia) susukii n. sp. is the earliest reported species of Meiocardia on the West Coast of North and South America.
Galeodea gallica, a species previously only known from lower Eocene strata in the Anglo-Paris Basin, is tentatively identified from the Maniobra Formation. Campanilopa dilloni, previously only known from south-central California, is present in the formation. Supplementary descriptions and illustrations are given for these two species.
The Maniobra species described have a close relationship to species characteristic of the Eurasian Tethyan paleobiogeographic province. The age of the Maniobra mollusks permits greater resolution of the timing of the westward migration of the Eurasian species, indicating that much of it occurred during early Eocene and/or late Paleocene time.