_Synonomy._--Geoffroy published a synopsis of the species he recognized (1809) prior to his formal description of the genus _Trionyx_ (1809a). Schweigger, nevertheless, probably was the first person to recognize the soft-shelled turtles as a distinct group, and he proposed for it the name _Amyda_ in an unpublished manuscript that he sent to Geoffroy. The latter author (1809a:15) relegated the name _Amyda_ to the synonomy of _Trionyx javanicus_ by means of the following entry: "_Amyda javanica._ Schweigger, dans un manuscript communique a l'Institut." Stejneger (1944:7) maintained that this publication of Schweigger's monotypic generic name clearly established its availability for the species congeneric with _Amyda javanica_ (= _Testudo cartilaginea_ Boddaert, 1770). Loveridge and Williams (1957:422) contend that this mere mention of the name _Amyda_ neither constitutes the proposal of a new name nor validates it, and that the first valid usage of the name _Amyda_ is that of Fitzinger (1835:120), who later (1843:30) designated the type species as _Amyda subplana_. The name _Amyda_ cannot date from _Oken_ (1816:348) as Volume 3 [Zoologie] of his Lehrbuch der Naturgeschichte published in 1815-1816 has been placed on the Official Index of Rejected and Invalid Works in Zoological Nomenclature with the Title No. 33; see Opinion 417 (Hemming, 1956). There has been considerable debate as to whether Geoffroy did or did not designate a type species of the genus _Trionyx_ (1809a). Although not specifically designated as the type species, _Trionyx aegyptiacus_ (= _Testudo triunguis_ Forskål) is considered by Smith (1930:2), Schmidt (1953:108, footnote), and Loveridge and Williams (1957:422) to have been sufficiently indicated by Geoffroy as the type species. But Stejneger (1944:6), H. M. Smith (1947:122), Conant and Goin (1948:11), and Mertens and Wermuth (1955) maintained that Geoffroy did not adequately designate a type species, and that Fitzinger (1843:30) designated the type species as _Trionyx granosus_ (= _Lissemys punctata_), a synonym of Geoffroy's species, _coromandelicus_. If Fitzinger's designation of a type species is accepted, the name _Trionyx_ is applicable to the forms herein referred to _Lissemys_, and _Amyda_ to the American forms. If Geoffroy's designation is accepted, the American forms are referable to _Trionyx_, and _Amyda_ is a synonym. The preceding includes only those generic names (listed in chronological order) that have been applied to Recent American soft-shelled turtles. Generic synonyms of the genus _Trionyx_ applicable to Old World species are listed by Stejneger (1907:514), Smith (1931:165), and Loveridge and Williams (1957:420-21). _Trionyx_ is the most widespread genus of the family; most of the species occur in southeastern Asia. All North American soft-shelled turtles belong to this genus.