A soft-shelled turtle that was obtained in the Sacramento River by three fishermen, near Sacramento, California, was named _Aspidonectes californiana_ by Rivers (1889:233). A comparison (with _Aspidonectes spinifer_ and _A. emoryi_) of certain features of the skull was largely prepared by Baur and included in the description (_op. cit._:234-35); seemingly, the most trenchant character of the skull of _californiana_ was the enlarged alveolar surfaces of the jaws. This feature prompted Baur (1893:220) to refer _californiana_ to the genus _Pelodiscus_, which also included _agassizi_ (skulls also having jaws with enlarged alveolar surfaces) and several Old World species. Van Denburgh (1917) discussed the origin of the specimen that formed the basis of River's description and concluded that it was brought over from China. Siebenrock (1924:192) and Mertens and Wermuth (1955:389) listed _Aspidonectes californiana_ as a synonym of _emoryi_. River's description is not that of _emoryi_; the enlarged alveolar surfaces of the jaws, and the dark carapace having tubercular ridges suggest a resemblance to _T. ferox_. The papillae on the neck are not found in any American species. Miller (1946:46, footnote 2) believed that "it obviously was introduced, apparently from China," and cited Pope (1935:61), who declared the specimen to represent _Trionyx sinensis_. Schmidt (1924:64) first reported the occurrence of _T. s. emoryi_ west of the continental divide in Arizona and suggested that it was highly probable that the species had been introduced near Phoenix in recent years. Cowles and Bogert (1936:42) mentioned a species of softshell occurring in the Boulder Dam region and presumed the species to be native to Asia and introduced by the Chinese. Linsdale and Gressitt (1937:222) determined the status of the species in the Colorado River drainage as _T. s. emoryi_. The discussions by Dill (1944:179-81) and Miller (1946:46) indicate that _emoryi_ was introduced into the Gila River (Colorado River drainage) in western New Mexico near the turn of the century. _T. s. emoryi_ and _T. ater_ are the only kinds of softshells occurring in México. The colloquial name for soft-shelled turtles in México is "tortuga blanca." This name is also used in reference to the Central American river turtle, _Dermatemys mawei_, which occurs on the east coast of México as far north as Veracruz. _Specimens examined._--Total 275, as follows: ARIZONA: _Maricopa_: CNHM 4768, KU 2214-19, 2803, 2824, 2837, 2903-07, 2909-16 (2914, 2 specimens), 2918-29, 3118-27, 3129, 3147-56, USNM 71627, Salt River, Phoenix. _Pinal_: UI 37713, Gila River, 6 mi. E Winkleman; UMMZ 92006-07, Gila River, 1/2 mi. below Coolidge Dam; UMMZ 105824, San Pedro River about 1 mi. above confluence with Gila River. NEVADA: _Clark_: AMNH 58370, Boulder City boat landing, Lake Mead; TU 15802, Virgin River, Mesquite.