Jesus Carranza (formerly Santa Lucrecia).--Lat. 17 deg. 27'; long. 95 deg. 02'; elev. 80 m. A town and railroad junction in the middle of the isthmus; rainforest [26]. Most of Dalquest's specimens came from varying distances from Jesus Carranza along the Rio Coatzacoalcos and its tributaries. Minatitlan.--Lat. 17 deg. 58'; long. 94 deg. 32'; elev. 15 m. An oil refinery center on the Rio Coatzacoalcos; savanna [20]. Naranjo.--Lat. 17 deg. 35'; long. 95 deg. 07'; elev. 100 m. A village on the Trans-isthmian Highway, 45 kilometers south of Acayucan; rainforest and palm forest [24]. Novillero.--Lat. 18 deg. 16'; long. 95 deg. 59'; elev. 10 m. A village on the Rio Papaloapan; scrub forest and grassland [9]. Oaxaquena, La.--Lat. 17 deg. 26'; long. 94 deg. 53'; elev. 80 m. A hacienda on the Rio Coatzacoalcos about 12 kilometers east of Jesus Carranza; rainforest [27]. Playas, Rio de las.--Lat. 18 deg. 08'; long. 94 deg. 07'; elev. 3 m. The river (sometimes known as the Rio Tonola) forming the boundary between the states of Veracruz and Tabasco; rainforest [18]. San Lorenzo.--Lat. 17 deg. 44'; long. 94 deg. 42'; elev. 25 m. A village on the Rio Chiquito, about 30 kilometers southeast of Acayucan; rainforest [23]. Suchil.--Lat. 17 deg. 31'; long. 95 deg. 03'; elev. 40 m. A village on the Trans-isthmian Railroad, about 10 kilometers north of Jesus Carranza; rainforest [25]. Tecolapan.--Lat. 18 deg. 24'; long. 95 deg. 18'; elev. 275 m. A village on a small river of the same name in the western foothills of Los Tuxtlas; rainforest [5]. Tejada, Lerdo de.--Lat. 18 deg. 37'; long. 95 deg. 31'; elev. 60 m. An agricultural village, 35 kilometers by road east-southeast of Alvarado; scrub forest, marshes, and sugar plantations [2]. Collections were made in a marsh, 5 kilometers west-northwest of the village. Tlacotalpan.--Lat. 18 deg. 37'; long. 95 deg. 42'; elev. 3 m. A town at the confluence of the Rio San Juan and Rio Papaloapan; marshes and sugar plantations [3]. Tula.--Lat. 18 deg. 36'; long. 95 deg. 22'; elev. 150 m. A village near the western base of Los Tuxtlas; low evergreen forest and marshes [4]. Collections were made in a marsh 3 kilometers northwest of the village. THE AMPHIBIAN FAUNA OF THE LOWLANDS In presenting an account of the amphibian fauna of the lowlands of the Isthmus of Tehuantepec three items must be considered: 1. The composition of the fauna. 2. The ecology of the fauna. 3. The distribution of the fauna. These items, together with similar data concerning the amphibians of the adjacent highlands, will form the basis for the subsequent discussion of the establishment of present patterns of distribution in the isthmian region. _Composition of the Fauna_