Measurements were taken in the manner described by Duellman (1956). Osteological data were obtained from specimens that were cleared in potassium hydroxide, stained with alizarin red, and stored in glycerine. Recordings were made by means of Magnemite portable tape recorders (Amplifier Corp. America). The calls recorded by Fouquette were analyzed on a Sonagraph (Kay Electric Co.) at the University of Texas; those recorded by Duellman were analyzed mainly on a Vibralyzer (Kay Electric Co.) at the University of Kansas and in part on a Sonagraph at the University of Southwestern Louisiana. Sample calls were analyzed on all three instruments; the slight differences in results were found to be less than the error in measurement, so the data from all sources were combined without correction. The techniques and terminology of the calls are those defined by Fouquette (1960a, 1960b).
In the accounts of the species we have attempted to give a complete synonymy. At the end of each species account the localities from which specimens were examined are listed alphabetically within each state, province, or department, which in turn are listed alphabetically within each country. The countries are arranged from north to south. Localities preceded by an asterisk (*) are not plotted on the accompanying maps due to the crowding of symbols that would have resulted. Abbreviations for museum specimens are listed below:
| AMNH | —American Museum of Natural History |
| ANSP | —Academy of Natural Sciences of Philadelphia |
| BMNH | —British Museum (Natural History) |
| BYU | —Brigham Young University |
| CAS | —California Academy of Sciences |
| FMNH | —Field Museum of Natural History |
| KU | —University of Kansas Museum of Natural History |
| MCZ | —Museum of Comparative Zoology |
| MVZ | —Museum of Vertebrate Zoology |
| SU | —Stanford University |
| UIMNH | —University of Illinois Museum of Natural History |
| UMMZ | —University of Michigan Museum of Zoology |
| USC | —University of Southern California |
| USNM | —United States National Museum |
| UU | —University of Utah |
| TCWC | —Texas Cooperative Wildlife Collection |
| TNHM | —Texas Natural History Museum |
HYLA MICROCEPHALA GROUP
Definition.—Small hylids attaining a maximum snout-vent length of 27 mm. in males and 32 mm. in females; dorsum yellowish tan with brown markings; thighs uniformly yellow, vocal sac in breeding males yellow; snout truncate in lateral profile; tympanum distinct, usually slightly smaller than one-half diameter of eye; vocal sac single, median, subgular; fingers about one-third webbed; toes webbed nearly to bases of discs, except only to middle of antepenultimate or base of penultimate phalanx of fourth toe; tarsal fold weak; inner metatarsal tubercle low, flat, elliptical; axillary membrane present; pupil horizontally elliptical; palpebral membrane unmarked; cranial elements reduced in ossification; sphenethmoid small, short; frontoparietal fontanelle large; tegmen tympani not extensive; quadratojugal greatly reduced; anterior arm of squamosal extending only about one-fourth distance to maxillary; posterior arm of squamosal not having bony connection with proötic; nasals lacking maxillary processes; medial ramus of pterygoid not having bony attachment to proötic; maxillary, premaxilary, and prevomerine teeth present; palatine and parasphenoid teeth absent; Mentomeckelians ossified; tadpoles having xiphicercal tails with deep caudal fins and terminal mouth lacking teeth; mating call consisting of one primary note followed by a series of shorter secondary notes; haploid number of chromosomes, 15 (known only in H. microcephala and H. phlebodes.)
Content.—As recognized here the Hyla microcephala group contains four species, one having two subspecies. An alphabetical list of the specific and subspecific names that we consider to be applicable to the Hyla microcephala group are listed below.
| Names Proposed | Valid Names |
| Hyla cherrei Cope, 1894 | ? = H. m. microcephala |
| Hyla microcephala Cope, 1886 | = H. m. microcephala |
| Hyla microcephala Boulenger, 1898 (nec Cope, 1886) | = H. microcephala underwoodi |
| Hyla microcephala martini Smith, 1951 | = H. microcephala underwoodi |
| Hyla microcephala sartori Smith, 1951 | = H. sartori |
| Hyla phlebodes Stejneger, 1906 | = H. phlebodes |
| Hyla robertmertensi Taylor, 1937 | = H. robertmertensi |
| Hyla underwoodi Boulenger, 1899 | = H. microcephala underwoodi |
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.