_T. ferox_ was considered to be indistinguishable from Lesueur's _Trionyx spiniferus_ (described in 1827), until Agassiz (1857:401) pointed out the differences between the two species. However, Agassiz (_op. cit._:402, Pl. 6, Fig. 3) regarded juveniles of _T. spinifer asper_ as the young of _ferox_. Consequently, the geographic range of _ferox_, as envisioned by Agassiz, extended from Georgia and Florida west to Louisiana. Neill (1951:15) considered all American forms conspecific. Crenshaw and Hopkins (1955) and Schwartz (1956) demonstrated that _ferox_ is a distinct species. Fitzinger (1843:30) designated the species _ferox_ as the type species of his genus _Platypeltis_ as follows: "Platypeltis. Fitz. Am[erica]. _Platypelt. ferox_. Fitz. Typus." If populations of soft-shelled turtles that are referable to _Testudo ferox_ Schneider are considered to comprise a distinct genus by future workers, _Platypeltis_ Fitzinger, 1835, is available as a generic name with _Testudo ferox_ Schneider, 1783, as the type species (by subsequent designation). _Trionyx ferox_ in the northern part of its range is sympatric with _T. spinifer asper_. In the region of overlap, the two species are nearly always ecologically isolated; _ferox_ inhabits lentic waters, whereas _T. s. asper_ is partial to lotic waters (Crenshaw and Hopkins, _op. cit._:16). There is no evidence of intergradation or hybridization. Many characters of _Trionyx ferox_ that are lacking in other North American forms are shared with some Asiatic softshells, such as the large size, longitudinal rows of tubercles that resemble ridges on the carapace, and the marginal ridge. It is thought that, of the living softshells in North America, _ferox_ is more closely allied to Old World forms of the genus than to _muticus_ or _spinifer_. Carr (1940:107) recorded _ferox_ from Okaloosa County, Florida, in the western end of the panhandle, whereas Crenshaw and Hopkins (1955:16) list the known westward extent of range as Leon and Wakulla counties. AMNH 6933 from west of the Apalachicola drainage in Washington County, Florida, tends to substantiate Carr's record, which is not included on the distribution map.