_Distribution._--_Hyla robertmertensi_ inhabits the Pacific slopes (to elevations of 700 meters) and lowlands from eastern Oaxaca (east of the Plains of Tehuantepec) southeastward to central El Salvador. The species also occurs in the Cintalapa Valley (Atlantic drainage) in southwestern Chiapas (Fig. 2.) The distribution seems to be limited on the northwest and southeast by arid environments. The region in which _Hyla robertmertensi_ lives is characterized by higher rainfall and more luxuriant vegetation than occur on the Plains of Tehuantepec or on the Pacific lowlands of eastern El Salvador and southern Honduras. In addition to the localities listed below, Mertens (1952:30) recorded the species from Hacienda Cuyan-Cuya, Depto. Sonsonate, El Salvador. [Illustration: Fig. 2. Map showing locality records for _Hyla robertmertensi_.] _Specimens examined._--490, as follows: +Mexico+: Chiapas: Acacoyagua, USNM 114754-61; *2 km. W Acacoyagua, UMMZ 87843 (28), 87844 (50), 87845 (50), 87846 (45), 87847 (27), 87848 (3); 32 km. N Arriaga, KU 57619-24, 59917-8 (skeletons); Asunción, FMNH 100413, 100501-4, UIMNH 26989-90, USNM 134267; *La Esperanza, USNM 114737-48, 114750-3, 17 km. S Las Cruces, KU 57625-49, 59997 (eggs); 8.5 km. N Puerto Madero, UMMZ 119981 (2); *11.7 km. N Puerto Madero, UMMZ 119982; Tapachula, FMNH 100096, UIMNH 26987; *11 km. S Tapachula, KU 57605-18, 59916 (skeleton); Tonolá, FMNH 27073, 100505-10, UIMNH 26988. Oaxaca: Tapanatepec, UMMZ 115245 (2), *1.6 km. E Tapanatepec, UMMZ 115244 (14); *4.3 km. E Tapanatepec, UIMNH 38368-9; *7.5 km. W Tapanatepec, UMMZ 115246 (39); 12.8 km. W Tapanatepec, KU 65007-14; 7.2 km. WNW Zanatepec, UMMZ 115243 (77); *13.6 km. WNW Zanatepec, TNHC 25213-22; 22.7 km. WNW Zanatepec, TNHC 25203-9. +Guatemala+: Jutiapa: Jutiapa, UMMZ 106848; La Trinidad, UMMZ 107733 (23). Retalhueleu: Casa Blanca, UMMZ 107732. +El Salvador+: La Libertad: 16 km. NW Santa Tecla, KU 44112. San Salvador: 21.9 km. N San Salvador, UMMZ 119983 (6). +Hyla phlebodes+ Stejneger _Hyla phlebodes_ Stejneger, Proc. U. S. Natl. Mus., 30:817, June 4, 1906 [Holotype.--USNM 2997 from "San Carlos," Costa Rica; Burgdorf and Schild collectors]. Taylor, Proc. Biol. Soc. Washington, 50:44, April 21, 1937; Univ. Kansas Sci. Bull., 35:888, July 1, 1952; Univ. Kansas Sci. Bull., 39:25, November 18, 1958. Fouquette, Evolution, 14:484, December 16, 1960. Duellman and Trueb, Univ. Kansas Publ., Mus. Nat. Hist., 17:348, July 14, 1966. _Hyla underwoodi_, Dunn, Occas. Papers Boston Soc. Nat. Hist., 5:413, October 10, 1931; Occas. Papers Boston Soc. Nat. Hist. 8:72, June 7, 1933; Amer. Mus. Novitiates, 747.2, September 17, 1934, Gaige, Hartweg, and Stuart, Occas. Papers Mus. Zool., Univ. Michigan, 357:5, October 26, 1937. Breder, 1946, Bull. Amer. Mus. Nat. Hist., 86:416, August 22, 1946.