Knowledge of early Tertiary nonmarine Mollusca of New Mexico is limited because of poor geographic records of type localities and lack of published re-examination of these mollusks and their stratigraphic relations. All published unequivocal early Tertiary records of Mollusca in New Mexico are from the Nacimiento (Paleocene) and San Jose (Eocene) Formations of northwestern Sandoval County. The five reported Nacimiento localities are probably Torrejonian (middle Paleocene), although a Puercan (early Paleocene) age for two of the localities cannot be ruled out. Nacimiento species include (* indicates species known only from type locality): Unio whitei? Henderson, Holospira grangeri Cockerell*, Pupa leidyi? Meek, Polygyra? petrochlora Cockerell*, Oreohelix nacimientensis (White), O. n. steini Cockerell*, Helix adipis White*, H. chriacorum Cockerell*, Viviparus meeki Wenz, V.. cf. V. conradi (Meek and Hayden), and Lioplacodes tenuicarinata? (Meek and Hayden). The reported occurrence of Helix hesperarche Cockerell in New Mexico is doubtful. The one reported San Jose locality is middle Wasatchian (middle early Eocene) in age. San Jose species include (* indicates species known only from type locality): Viviparus calamodontis (Cockerell)*, and Goniobasis carteri Conrad. Nonmarine mollusks from the Raton Formation in Colfax County and Ringbone Formation of southern Gran County may be of Late Cretaceous or early Tertiary age. The Raton and Ringbone mollusks are not temporally diagnostic, but do indicate a nonmarine environment for the enclosing sediments.

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