The vegetation of northern and central El Petén has been studied by Lundell (1937), who made only passing remarks concerning the plants of the southern part of El Petén. No floristic studies have been made there. The following remarks are necessarily brief and are intended only to give the reader a general picture of the forest. I have included names of a few of the commoner trees that I recognized. Chinajá is located in a vast expanse of unbroken rainforest. In this forest there is a noticeable stratification of the vegetation. Three strata are apparent; in the uppermost layer the tops of the trees are from 40 to 50 meters above the ground. The spreading crowns of the trees and the interlacing vines form a nearly continuous canopy over the lower layers. Among the common trees in the upper stratum are _Calophyllum brasiliense_, _Castilla elastica_, _Cedrela mexicana_, _Ceiba pentandra_, _Didalium guianense_, _Ficus_ sp., _Sideroxylon lundelli_, _Swietenia macrophylla_, and _Vitex_ sp. (Pl. 1, fig. 1). The middle layer of trees have crowns about 25 meters above the ground; these trees in some places where the upper canopy is missing form the tallest trees in the forest. This is especially true on steep hillsides. Common trees in the middle layer include _Achras zapote_, _Bombax ellipticum_, _Cecropia mexicana_, _Orbignya cohune_, and _Sabal_ sp. The lowermost layer reaches a height of about 10 meters; in many places in the forest this layer is absent. Common trees in the lower stratum include _Crysophila argentea_, _Cymbopetalum penduliflorum_, _Casearia_ sp., and _Hasseltia dioica_. The ground cover is sparce; apparently only a few small herbs and ferns live on the heavily shaded forest floor. Important herpetological habitats include the leaf litter, rotting stumps, and rotting tree trunks on the forest floor and the buttresses of many of the gigantic trees, especially _Ceiba pentandra_ (Pl. 2). Epiphytes, especially various kinds of bromeliads, are common. Most frequently these are in the trees in the upper and middle strata. At Toocog there is sharp break between savanna and forest (Pl. 7, fig. 2). The forest is noticeably drier and more open than at Chinajá (Pl. 9). The crowns of the trees are lower, and there is no nearly continuous canopy between 40 and 50 meters above the ground. Although _Swietenia macrophylla_ and other large trees occur, they are less common than at Chinajá. Especially common at Toocog are _Achras zapote_, _Brosimum alicastrum_, and various species of _Ficus_. GAZETTEER The localities from which specimens were obtained are cited below and shown on the accompanying map (Fig. 1). [Illustration: FIG. 1. Map of El Petén, Guatemala, showing localities mentioned in text.]