TEXAS: _Bosque_: Bosque River, "near" Valley Mills (Strecker, 1928:6). _Harris_: Addicks (Brown, 1950:250). _Henderson_: Cedar Creek (Strecker, 1926a:7). _Jefferson_: 12 mi. SW Port Arthur (Guidry, 1953:56). _Liberty_: Daisetta (Brown, _loc. cit._); San Jacinto River (Strecker, 1915:15). _McLennan_: "near" Crawford (Brown, _loc. cit._). _Orange_: 1 mi. N Bridge City (Guidry, _loc. cit._). _Tarrant_: Trinity River, Fort Worth (Stejneger, 1944:66). _Taylor_: Abilene (KKA). _Tyler_: Colmisneil (Siebenrock, 1909:603). _Walker_: 6 mi. E Huntsville (TCWC 329, listed in card file). _Wheeler_: 5 mi. N Wheeler (Brown, _loc cit._). =Trionyx ater= Webb and Legler Black Softshell _Trionyx ater_ Webb and Legler, Univ. Kansas Sci. Bull., 40:21, pls. 1 and 2, 1960, April 20. _Type._--Holotype, KU 46903, alcoholic female; obtained 16 km. S Cuatro Ciénegas, Coahuila, México, by John M. Legler (and party), September 6, 1958. _Range._--Basin of Cuatro Ciénegas, central Coahuila, Mexico (see map, Fig. 22). _Diagnosis._--Posterior margin of carapace of some females having fine corrugations, edge often ragged, and no pale outer margin; septal ridges reduced in adult males; over-all dorsal coloration (in preservative) dark, lacking contrasting patterns. _Description._--Plastral length of adult male, 9.6 centimeters (KU 46911); of largest female, 18.4 centimeters (KU 46903). Adult male: anterior edge of carapace smooth; septal ridges reduced; pale outer rim, and small, whitish, dots posteriorly on carapace; surface of carapace slightly gritty or sandpapery posteriorly; snout broadened; over-all dorsal coloration dark gray or slate; contrasting pattern on soft parts of body lacking; ventral surface whitish having few blackish marks posteriorly on undersurface of carapace. Females: posterior margin of carapace usually having fine corrugations; edge of carapace posteriorly often ragged; pale rim of carapace absent; mottled and blotched pattern not contrasting on blackish carapace; dorsal surface of soft parts of body dark gray or slate, lacking contrasting pattern; ventral surface of carapace and posterior part of plastron usually having many blackish flecks and markings; tubercles lacking on anterior edge and in center of carapace posteriorly; septal ridges well developed. Medial angle of epiplastron (as observed through overlying skin) bent at angle of approximately 90 degrees. Other osteological characters presumably as in _spinifer_. Range in length of plastron (cm.) of 11 females (mean follows extremes); 10.8-18.4, 15.0; proportional measurements of 12 specimens (including adult male, mean follows extremes): PL/HW, 4.70-5.43, 4.93; CL/CW, 1.28-1.43, 1.32; CL/PCW, 1.98-2.42, 2.15; HW/SL, 1.22-1.58, 1.37; CL/PL, 1.29-1.44, 1.36; some females (especially KU 46908) have noticeably elongate carapaces.