only one named species of Clidastes that is valid, C. propython. Clidastes iguanavus Cope, 1868 was the original type species, but the ICZN was petitioned to make C. propython the new type species by virtue of that species being based on diagnostic remains, which it did vis-à-vis Opinion 1750 (1993). Invalid species There is also an undescribed form from the Mooreville Chalk Formation of Alabama that likely represents a new taxon on its own, informally dubbed "Clidastes moorevillensis", which can be distinguished from both C. propython and C. liodontus based on its dental characteristics. Clidastes liodontus was described from the late Coniacian to early Campanian Smoky Hill Chalk Member of the Niobrara Formation in Kansas. There are also earlier occurrences of the species, dated to the Coniacian, and it might thus be ancestral to the later C. propython. C. liodontus grew to about 3–4 meters in length compared to the 4-5 meter (and on occasion larger) length of C. propython. The type specimen of C. liodontus, consisting of maxillae, a premaxilla and dentaries from the Niobrara Formation of Kansas, was housed at the Bayerische Staatssammlung für Paläontologie and may have been destroyed in the Second World War. Russell (1967) diagnosed the species in general as follows: "Premaxilla “V”-shaped in horizontal cross-section, small rostrum present anterior to premaxillary teeth. Posteroventral portion of root of second premaxillary tooth not exposed on sutural surface with maxilla. Premaxillo-maxillary suture rises posteriorly to position varying from dorsal to fourth to dorsal to sixth maxilIary tooth and parallels longitudinal axis of cranium. Fourteen to fifteen teeth in maxilla. Median dorsal surlace of parietal narrow. Parietal foramen small, close to or distinctly separated from frontal suture. Parietal foramen opens ventrally into brain cavity without broadening into wide excavation. Anterior border of prootic descends beneath prootic incisure without forming shelf. Foramen for cranial nerve VII leaves brain cavity through medial wall of prootic. Infrastapedial process absent on quadrate. Sixteen teeth in dentary." Lively (2019) declared Clidastes liodontus a nomen dubium, while taking note of the nomen nudum status of "moorevillensis", recommending that Clidastes be restricted to C. propython. Clidastes propython C. propython is the best studied species of the genus, and was for this reason chosen by the ICZN to replace C. iguanavus as the type species. C. propython is known from the Campanian of the United States (Alabama, Colorado, Texas, Kansas and South Dakota) and of Sweden.