| Population | N | Shanks | Interorbital bar | Dorsolateral stripe | Scapular markings | Sacral markings | ||||||||||||
| Bars | Flecks | Present | Absent | Groin | Sacrum | X | )( | ][ | Other | /\ | / \ | Other | ||||||
| Oaxaca: Donají-Sarabia | 27 | 22 | 5 | 27 | 0 | 0 | 27 | 23 | 4 | 0 | 0 | 7 | 6 | 14 | ||||
| Tabasco: Teapa-Villahermosa | 55 | 46 | 9 | 55 | 0 | 0 | 55 | 53 | 2 | 0 | 0 | 19 | 11 | 23 | ||||
| Guatemala: La Libertad | 51 | 51 | 0 | 51 | 0 | 17 | 34 | 45 | 6 | 0 | 0 | 16 | 14 | 21 | ||||
| Guatemala: Finca Chamá | 32 | 32 | 0 | 32 | 0 | 0 | 32 | 32 | 0 | 0 | 0 | 26 | 2 | 4 | ||||
| Guatemala: Puerto Barrios | 31 | 31 | 0 | 31 | 0 | 14 | 17 | 23 | 0 | 4 | 4 | 6 | 4 | 21 | ||||
| Honduras: Lago Yojoa | 13 | 13 | 0 | 13 | 0 | 9 | 4 | 3 | 2 | 3 | 5 | 2 | 1 | 10 | ||||
| Nicaragua: La Cumplida | 56 | 44 | 12 | 54 | 2 | 13 | 43 | 11 | 35 | 8 | 2 | 0 | 19 | 37 | ||||
| Nicaragua: Tipitapa | 10 | 10 | 0 | 10 | 0 | 8 | 2 | 0 | 5 | 3 | 2 | 0 | 3 | 7 | ||||
| Nicaragua: Santo Thomás | 10 | 10 | 0 | 10 | 0 | 8 | 2 | 3 | 0 | 7 | 0 | 0 | 5 | 5 | ||||
| Costa Rica: Tenorio-Tilarán | 12 | 0 | 12 | 6 | 6 | 7 | 5 | 0 | 0 | 12 | 0 | 0 | 0 | 12 | ||||
| Costa Rica: Las Cañas-Liberia | 38 | 21[A] | 15 | 34 | 4 | 25 | 13 | 0 | 11 | 19 | 8 | 0 | 0 | 38 | ||||
| Costa Rica: Esparta | 32 | 26 | 6 | 29 | 3 | 30 | 2 | 0 | 0 | 14 | 18 | 0 | 0 | 32 | ||||
[A] Longitudinal stripes present in two specimens.
When this frog is active at night its dorsum is pale yellow; faint flecks are present in some individuals. The white dorsolateral line usually is evident in the tympanic region, but in many individuals a dorsal pattern of lines and other marks is not evident. By day the dorsum changes to yellowish tan or pale brown with dark brown or reddish brown markings ([Pl. 13]). The venter is white, and the vocal sac in breeding males is yellow. The iris is pale bronze with a brown tint anterior and posterior to the pupil.
Remarks.—Hyla microcephala underwoodi has had a confused nomenclatural history. The taxon was first named Hyla microcephala by Boulenger (1898); this name was preoccupied by Hyla microcephala Cope (1886). Cole and Barbour (1906) and Kellogg (1932) used the name Hyla phlebodes Stejneger (1906) for specimens of this frog from México. Dunn (1931, 1933, 1934) applied the name Hyla underwoodi to Panamanian specimens that we identify as Hyla phlebodes. Smith (1951) named Hyla microcephala martini from southern México and Guatemala and considered the northern populations to represent a subspecies distinct from the Costa Rican Hyla microcephala underwoodi, despite the fact the Stuart (1935:39) stated that comparisons of specimens from El Petén, Guatemala, with the holotype of Hyla underwoodi showed only trivial differences.
Much of the confusion regarding the name Hyla underwoodi stems from the illustration given by Boulenger (1898:pl. 39, fig. 3) and reproduced by Taylor (1952:892), which shows a frog having a unicolor dorsum, dorsolateral white lines, and dark flanks. This pattern is in marked contrast to the pattern seen in most preserved specimens, which have the dorsum variously marked by dark brown lines or irregular marks. Smith (1951:185), in his description of Hyla microcephala martini from southern México, considered H. underwoodi to be a subspecies of H. microcephala that lacked dorsal dark markings.
Data accumulated in 1961 through field studies by the senior author at the type locality, Bebedero, and other localities in Guanacaste and Puntarenas provinces in Costa Rica provide a reasonable explanation of the differences in color pattern. As noted in the preceding description of this subspecies, at night the dorsal markings are not evident in many living individuals, whereas by day the dorsal markings are prominent. Most collectors prepare their specimens by day; consequently the majority of specimens have a pronounced dorsal pattern. Of the frogs collected in Costa Rica in 1961, some specimens were preserved at night; others from the same series were preserved by day. The differences are striking. In those preserved at night, dorsal markings are faint, if present at all. Some specimens closely match the figure given by Boulenger (1898).
It is extremely doubtful if the frog described and illustrated by Boulenger could be associated with either Hyla phlebodes or H. microcephala microcephala. Individuals of the former species lack a dorsolateral white line and always have some dorsal markings evident at night; furthermore, H. phlebodes is not known to occur on the Pacific lowlands. Hyla microcephala microcephala occurs farther southeast. Since there is no reason to doubt the type locality of H. underwoodi, since specimens from the area around the type locality that have been preserved at night are like the holotype in pattern, and since the characteristics of the populations of the frogs in Guanacaste are the same as, or gradually blend into those of, populations in northern Central America and southern México, the frogs from throughout the entire range can be referred to one taxon, the earliest name for which is Hyla underwoodi Boulenger, which herein is considered to be a subspecies of H. microcephala Cope.
Distribution.—Hyla microcephala underwoodi inhabits the Atlantic slopes and lowlands from southern Veracruz and extreme northern Oaxaca eastward across the base of the Yucatan Peninsula (possibly the species is extant in the northern part of the peninsula) to British Honduras and thence southeastward through the Caribbean lowlands and interior valleys in Honduras to central Nicaragua, where it apparently avoids the forested Caribbean lowlands and the dry Pacific lowlands of northwestern Nicaragua, but in the vicinity of Managua invades the Pacific lowlands and continues southward into northwestern Costa Rica as far as the Puntarenas Peninsula ([Fig. 1]). In México and Guatemala the species has not been taken at elevations of more than 350 meters, whereas farther south it occurs at higher elevations—780 meters at Silencio, Costa Rica, 830 meters on Montaña de Guaimaca, Honduras, 960 meters at Finca Tepeyac, Nicaragua, and 1200 meters at Finca Venecia, Nicaragua.
Specimens examined.—1270, as follows: Mexico: Campeche: Balchacaj, FMNH 100406, UIMNH 20944-6; Encarnación, FMNH 27069-70, 75784, MCZ 28360, 29637, UIMNH 20948-58, 20965, USNM 134264-5; Escárcega, UMMZ 122999; *7.5 km. W Escárcega, KU 71229-43; Laguna Alvarado, 65 km. S Xpujil, KU 75084-9; Pacaitún, Río Candelaria, FMNH 83118-20; *Tres Brazos, FMNH 113101-22, UIMNH 20947; 10 km. W Xpujil, KU 75082-3. Chiapas: Palenque, UIMNH 47984, 49139-50, USNM 114973-8. Oaxaca: *5 km. N Chiltepec, KU 87015-23; 3 km. N Donají UMMZ 115249 (9); *3.7 km. N Donají, UMMZ 115250 (5); *43 km. N Matías Romero, UIMNH 42550-68; *3.5 km. N Palomares, TNHC 25185, 25321-31, 25341-68; 4.6 km. N Sarabia, UMMZ 115247 (2); *6.1 km. N Sarabia, UMMZ 115248 (11), *3 km. N Tolocita, KU 39655; Tuxtepec, KU 87024-40. Tabasco: 24 km. N Frontera, MCZ 35665-70; 0.8 km. E Río Tonolá, TNHC 25189; Teapa, UMMZ 119218 (4); *2.7 km. N Teapa, UMMZ 119216 (4); *10 km. N Teapa, UMMZ 119217 (6); *11.5 km. N Teapa, UMMZ 119219; *15.2 km. N Teapa, UMMZ 119220 (4); *17.6 km. N Teapa, UMMZ 119221 (12), 3.3 km. S Villahermosa, UMMZ 119215 (12), *17.6 km. S Villahermosa, UMMZ 119214 (12). Veracruz: 2.1 km. N Acayucan, UIMNH 42547-9; *6.4 km. NW Acayucan, UMMZ 115254 (14); 1.6 km. ESE Alvarado, UMMZ 115258 (39); *2.4 km. ESE Alvarado, UMMZ 115251 (2); *4.5 km. S Aquilera, [UMMZ]115252 (21); *8 km. SW Coatzacoalcos, UMMZ 119213 (10); 2.2 km. E Cosoleacaque, UMMZ 119222 (26); 10 km. SE Hueyapan, UMMZ 115255; 0.8 km. S Lerdo de Tejada, UMMZ 122778; *3.6 km. NE Minatítlán, TNHC 25150-2; 1.9 km. S Naranja, UMMZ 115253 (3); 4.5 km. NE Novillero, UMMZ 115256; San Andrés Tuxtla, FMNH 113124-8, UIMNH 20942-3. Yucatán: Chichén-Itzá, FMNH 36570, MCZ 2463 (2).