Epiphytes, especially the bromeliads, provide refuge for a variety of tree frogs and small snakes. Of the tree frogs, _Hyla picta_, _Hyla staufferi_, _Phyllomedusa callidryas taylori_, _Similisca baudini_, and _Similisca phaeota cyanosticta_ have been found in bromeliads; other species probably occur there. Among the snakes, _Imantodes cenchoa leucomelas_, _Leptodeira frenata malleisi_, _Leptodeira septentrionalis polysticta_, _Sibon dimidiata dimidiata_, and _Sibon nebulata nebulata_ are frequent inhabitants of bromeliads; all of these snakes are nocturnal. Relationships of the Fauna Most of the 78 species of amphibians and reptiles definitely known from the rainforest in southern El Petén have extensive ranges in the Atlantic lowlands of southern México and Central America; many extend into South America. Sixty-two (80%) of the species belong to this group having extensive ranges in Middle America. Three species (_Syrrhophus leprus_, _Leptodeira frenata_, and _Kinosternon acutum_) are at the southern limits of their distributions in southern El Petén and northern Alta Verapaz, whereas _Eleutherodactylus rostralis_ and _Thecadactylus rapicaudus_ are at the northern and western limits of their distributions in El Petén. Nine (11%) species have the center of their distributions in El Petén and the Yucatán Peninsula; representatives of this group include _Claudius angustatus_, _Dermatemys mawi_, _Laemanctus deborrei_, and _Eumeces schwartzei_. In determining a measure of faunal resemblance, I have departed from the formulae discussed by Simpson (1960) and have analyzed the degree of resemblance by the following formula used to calculate an index of faunal relationships: C (2) / (N_{1} + N_{2}) = R, where C = species common to both faunas. N_{1} = number of species in the first fauna. N_{2} = number of species in the second fauna. R = degree of relationships (when R = 1.00, the faunas are identical; when R = 0, the faunas are completely different).