Late Cretaceous and Paleogene freshwater gastropods from Northeastern Mexico

Twenty-three species of Campanian, Maastrichtian, Paleocene, and Eocene freshwater gastropods from northeastern Mexico are described, including eight new species: Viviparus mcbridei, Pachychilus (Pachychiloides) lawtoni, Melanoides (Melanoides) yolandae, Melanoides (Melanoides) wollebeni, Physa cepedaensis, Mesolanistes magnus, Mesolanistes murrayi, and Gyraulus zoltani. Specimens were collected from fine-grained, green sandstone and mudstone, red mudstone, and as hematized remains in fine light-brown sandstones belonging to the following stratigraphic units of northeastern Mexico: Cerro del Pueblo (Campanian, Parras Basin), Olmos (Maastrichtian, Sabinas Basin), Las Enemas (Paleocene, Parras Basin), and Carroza (Eocene, La Popa Basin) Formations. All except two of the genera (?Pyrgulifera and Mesolanistes) have recent representatives. Review of habitats of living species of the six extant genera and interpretations of sample lithologies support the inference of dominantly freshwater paleoenvironments. Only one Maastrichtian locality is interpreted confidently to have had a brackish water influence.