The herpetofauna of southern El Petén has been compared with that in the Tikal-Uaxactún area (Stuart, 1958), that in the humid lowlands of Alta Verapaz (Stuart, 1950, plus additional data), and that in the Mexican state of Yucatán (Smith and Taylor, 1945, 1948, and 1950). The herpetofaunas of lowland Alta Verapaz and Yucatán are the largest, having respectively 94 and 91 species, where as there are 78 species known from southern El Petén and 64 from the Tikal-Uaxactún area. An analysis of faunal relationships (Table 2) shows that the faunas of the rainforests of southern El Petén and lowland Alta Verapaz are closely related. The relationships between these two areas and the Tikal-Uaxactún area in northern El Petén is notably less. Apparently the biggest faunal changes take place between southern El Petén and the Tikal-Uaxactún area, and between the latter and Yucatán. As stated by Stuart (1958:7) the Tikal-Uaxactún is transitional between the humid rainforests to the south and the dry outer end of the Yucatán Peninsula. The transitional nature of the environment is exemplified by a rather depauperate herpetofauna consisting of some species of both dry and humid environments and lacking a large fauna typical of either. Contrariwise, the continuity of the environment from southern El Petén to the lowlands of Alta Verapaz is reflected in degree of resemblance of the herpetofaunas. TABLE 2.--INDEX OF FAUNAL RELATIONSHIPS BETWEEN SOUTHERN EL PETÉN AND OTHER REGIONS. ======================+==========+==========+==========+========== | Lowland | Southern | Tikal- | | Alta | El | Uaxactún | Yucatán | Verapaz | Petén | Area | ----------------------+----------+----------+----------+---------- Lowland Alta Verapaz | | .85 | .61 | .43 ----------------------+----------+----------+----------+---------- Southern El Petén | .85 | | .64 | .41 ----------------------+----------+----------+----------+---------- Tikal-Uaxactún Area | .61 | .64 | | .63 ----------------------+----------+----------+----------+---------- Yucatán | .43 | .41 | .63 | ----------------------+----------+----------+----------+---------- Most of the species of amphibians and reptiles found in southern El Petén are found in humid tropical forests from the Isthmus of Tehuantepec southeastward on the Atlantic lowlands well into Central America. ACCOUNTS OF SPECIES