Although actually located in the region of the Isthmus of Tehuantepec, the Sierra de los Tuxtlas, because of its isolated position, need not be considered in great detail in analyzing the distribution of animals inhabiting the lowlands of the isthmus. Nevertheless because some species living in the highlands adjacent to the isthmus also live in the Tuxtlas, this range is briefly described here. The Sierra de los Tuxtlas is a range of volcanos lying near the Gulf Coast in southern Veracruz between the mouths of the Rio Papaloapan and the Rio Coatzacoalcos. Volcan San Martin, the highest peak, rises above 1800 meters. This range of volcanos is surrounded by lowlands, which immediately to the south and west are covered with savanna and in places by scrub forest. The luxuriant nature of the vegetation on these volcanos indicates that this range receives much more rainfall than the surrounding lowlands. Especially on the northern slopes, tropical rainforest is well developed; this is replaced at about 1200 meters by cloud forest. The southern and western slopes are drier, for the lower slopes are covered with a scrubby, but evergreen, forest. Detailed comments on the herpetofauna of the Tuxtlas have been omitted purposefully, for the reptiles and amphibians of the region currently are being studied by Douglas Robinson. GAZETTEER The following localities are those referred to in the text. The name of the locality (listed alphabetically by states) is followed by latitude, longitude, elevation, general description (town, ranch, etc.), and general type of habitat. Unless otherwise noted, distances are straight-line (airline) distances in kilometers. The localities have been plotted from the American Geographical Society's "Map of Hispanic America on the Scale of 1:1,000,000" (Millionth Map). Numbers in brackets identify the position of a locality on the accompanying map (Fig. 1). _Oaxaca_ Agua Caliente.--Lat. 16 deg. 38'; long. 94 deg. 48'; elev. 140 m. A hot spring, 6.9 km. north of La Ventosa on the Trans-isthmian Highway; arid scrub forest [43]. Arenal, Cerro de.--Lat. 16 deg. 18'; long. 95 deg. 32'; elev. 925 m. (crest). A ridge northeast of Tenango; scrub forest on slopes and pine-oak forest on top [64]. Barrio, El.--Lat. 16 deg. 38'; long. 95 deg. 07'; elev. 314 m. A village about 10 kilometers southwest of Matias Romero; transition between scrub forest and broadleaf hardwood forest [38]. Bisilana.--Lat. 16 deg. 20'; long. 95 deg. 13'; elev. 35 m. A place name for a former ranch at the edge of Tehuantepec; open arid scrub forest [62]. Chivela.--Lat. 16 deg. 20'; long. 95 deg. 01'; elev. 195 m. A village on the Trans-isthmian Railroad, 26 kilometers by rail south of Matias Romero and on the western edge of the semi-arid Plains of Chivela [40].