We describe a new extinct genus and species of bat belonging to the endemic Neotropical family Natalidae (Chiroptera) from the Thomas Farm Local Fauna in northern peninsular Florida of early Miocene age (18–19 million years old). The natalid sample from Thomas Farm consists of 32 fossils, including a maxillary fragment, periotics, partial dentaries, isolated teeth, humeri, and radii. A proximal radius of an indeterminate natalid is reported from the I-75 Local Fauna of early Oligocene age (about 30 million years old), also from northern Florida. These fossils from paleokarst deposits in Florida represent the 1st Tertiary records of the Natalidae. Other extinct Tertiary genera previously referred to the Natalidae, including Ageina, Chadronycteris, Chamtwaria, Honrovits, and Stehlinia, may belong to the superfamily Nataloidea but do not fit within our restricted definition of this family. Eight derived characters of the Natalidae sensu stricto are discussed, 5 of which are present in the new Miocene genus. Intrafamilial phylogenetic analysis by parsimony of the Natalidae suggests that the 3 living subgenera, Natalus (including N. major, N. stramineus, and N. tumidirostris), Chilonatalus (including C. micropus and C. tumidifrons), and Nyctiellus (including N. lepidus), deserve full generic rank. The Natalidae apparently evolved in North America before the late Oligocene, went extinct in what is now the Nearctic region (i.e., Florida) after the early Miocene, and survived in tropical Middle America during the remainder of the Tertiary. The presence of 2 endemic genera and 4 endemic species suggests that natalids reached the West Indies by overwater dispersal early in their history (Oligocene or Miocene). The lack of a Tertiary fossil record, marginal distribution, and limited species richness and endemism of natalids in South America are suggestive of a comparatively late arrival on that continent, possibly in the late Pliocene after the beginning of the Great American Faunal Interchange.