Most specimens from the lower Atchafalaya River drainage are referable to _pallidus_. Eastward, intergradation occurs with the _spinifer-hartwegi_ population; USNM 100089-90 from Assumption Parish, near Napoleonville, Louisiana, are referred to _pallidus_. TU 11983, from Bayou Lafourche, Raceland, La Fourche Parish, and TU 13698.11, from Bayou Gauche in St. Charles Parish, Louisiana, are juvenal males that combine the characteristics of _pallidus_ and _hartwegi_; the carapaces are covered with blackish spots and posteriorly have distinct whitish dots. The population in the Atchafalaya River more closely resembles _pallidus_ than it does _hartwegi_ or _spinifer_. In former times the Atchafalaya River was presumably continuous solely with the Red River (inhabited by _pallidus_). Now, these two rivers and the Mississippi River are interconnected in east-central Louisiana. A large volume of water of the Mississippi drainage is conveyed to the Gulf of Mexico by the Atchafalaya, and someone has said that by approximately 1975, unless man interferes, two-thirds to three-fourths of the total volume of water of the Mississippi River will be drained by the Atchafalaya. One can expect, therefore, an increase in the influence of the _hartwegi-spinifer_ population in the Atchafalaya River drainage. _Specimens examined._--Total 270, as follows: ARKANSAS: _Lafayette_: KU 2930-37, 2939-40, 2942, 2944 (two of three specimens bear this catalog number), 2945-57, 2958 (2), 2959-61, 2963 (two of three specimens bear this catalog number), 2964 (one of two specimens bears this catalog number), 2965-73, 2987-89, 3056, Lewisville. LOUISIANA: _Acadia_: USNM 100151-59, Mermentau River. _Assumption_: USNM 100089-90, Bayou Lafourche, "near" Napoleonville. _Beauregard_: TU 1231-32, 1253-55, 1291, 13211, 13266, Sabine River, 8 mi. SW Merryville. _Bienville_: TU 5649-50, Lake Bistineau. _Caddo_: TU 381, 397-99, 469-72, 474-90, 678, 10170, Caddo Lake: TU 15818-19, Cross Lake. _Calcasieu_: UMMZ 92754, 5 mi. W Iowa. _Cameron_: TU 1122, Lacassine Wildlife Refuge. _Concordia_: USNM 99862-64, 99866-69, 99871-75, Red River, "near" Shaw. _De Soto_: SM 2374-75, Wallace Bayou. _Grant_: TU 5647, Lake Iatt. _Iberville_: USNM 83985, 2 mi. E Mounds; USNM 100239-41, Grand Lake west of White Castle; USNM 100380, Plaquemine; USNM 100412, 100414-15, 100419, Spanish Lake, "near" St. Gabriel. _Jefferson Davis_: Calcasieu River drainage, WTN (no number, see page 524). _Natchitoches_: TU 5763, Bermuda; USNM 100421, "near" Natchitoches. _Sabine_: TU 13210, 13212-13, 13265, 13280-82, 13303-06, Sabine River, 8 mi. SW Negreet. _St. Martin_: USNM 100160, Bayou Chene; USNM 100650, Atchafalaya. _St. Mary_: USNM 100395-97, 100404, 100409-10, Berwick Bay near Morgan City.