_Discussion._--The color pattern is the most useful character in distinguishing the species of the _Hyla microcephala_ group from one another. Except in _Hyla microcephala_, little geographic variation in color pattern is noticeable. The features of color pattern that are helpful in identifying the species are: 1) presence or absence of lateral dark brown stripe; 2) longitudinal extent and width of lateral stripe, if present; 3) presence or absence of a narrow white line just dorsal to the lateral dark stripe; 4) presence or absence of an interorbital dark mark; 5) the arrangement of dark markings on the back, either as longitudinal lines or series of dashes, or in the form of various kinds of transverse markings; 6) presence of dark flecks, longitudinal line, or transverse marks on shanks. Few consistent differences in measurements and proportions exist among the species (Table 1). The most obvious morphological difference is that the head is noticeably narrower in _H. robertmertensi_ than in the other species. _Hyla phlebodes_ is the smallest species; adult males attain snout-vent lengths of only 23.6 mm. The body is slender in _H. microcephala_ and _robertmertensi_, slightly wider in _phlebodes_, and noticeably broader in _sartori_. _Distribution._--The composite range of the Middle American frogs of the _Hyla microcephala_ group includes the lowlands of southern México and Central America, in some places to elevations of 1200 meters, southeastward from southern Jalisco and southern Veracruz, excluding arid regions (northern Yucatán Peninsula, Balsas-Tepalcatepec Basin, Plains of Tehuantepec, Grijalva Valley, Salamá Basin, and upper Motagua Valley) to the Pacific lowlands and the Cauca and Magdalena valleys in Colombia. Key to Species and Subspecies 1. Lateral dark stripe, bordered above by narrow white line, extending from snout at least to sacral region 2 Lateral dark stripe, if present, not extending posteriorly to sacral region and not bordered above by narrow white line 4 2. Lateral dark stripe continuous to groin; dark flecks or longitudinal line on shanks; interorbital dark bar absent; dorsal pattern usually consisting of pair of longitudinal dark lines or series of dashes 3 Lateral dark stripe usually extending only to sacral region; dark transverse bars on shanks; interorbital bar usually present; dorsal pattern usually consisting of interconnecting dark lines, sometimes forming transverse marks _H. microcephala underwoodi_ 3. Lateral dark stripe narrow, covering only upper edge of tympanum; dorsal longitudinal stripes continuous, extending to vent _H. microcephala microcephala_