The similarity in size of _Bufo marmoreus_ and _valliceps_ and their almost completely allopatric ranges suggest that the two species may be in competition at any one locality. Nevertheless, both were calling from a small rocky stream south of Santiago Chivela on July 6, 1956. On the night of July 6, 1958, an estimated 400 toads of this species made up a breeding congregation near Salina Cruz. The site was a shallow muddy pond about 20 x 40 meters located in an area cleared of scrub forest; the banks of the pond were devoid of vegetation (Pl. 5, fig. 2). Breeding in the same pond were _Rhinophrynus dorsalis_ and _Diaglena reticulata_. The following morning no more than a dozen _Bufo_ were found in the pond, but several individuals were found beneath debris and in small burrows near the pond. On July 7, 1958, large numbers of tadpoles and recently metamorphosed young were in a shallow grassy pool just east of Salina Cruz. Taylor (1943b:347) referred certain specimens from Tehuantepec to _Bufo perplexus_, a species closely related to _Bufo marmoreus_. Evidence to be presented elsewhere shows that _perplexus_ does not occur in the isthmus. =Bufo valliceps valliceps= Wiegmann _Oaxaca_: Guichicovi (2); Matias Romero; 32 km. N of Matias Romero (2); Nueva Raza; Rio Sarabia (3); Santa Maria Chimalapa (14); Santiago Chivela; 12 km. S of Santiago Chivela (5); Santo Domingo (5); Tolosita (7). _Veracruz_: Acayucan (3); Alvarado; Amatitlan; Ayentes; Cosamaloapan (3); Cosoleacaque (6); Cuatotolapam (14); Hueyapan; 20 km. ENE of Jesus Carranza (6); 20 km. S of Jesus Carranza; 25 km. SE of Jesus Carranza (23); 35 km. SE of Jesus Carranza; 60 km. SW of Jesus Carranza (5); La Oaxaquena (4); Novillero (4); San Lorenzo (5). Individuals were found in both wet and dry seasons. In the dry season they were most frequently found in rainforest, whereas in the rainy season breeding congregations were found in savannas as well. This toad occurs throughout the Gulf lowlands and on the Pacific slopes and in the Grijalva Valley of Chiapas and Guatemala, but not on the Pacific lowlands of the isthmus. I have not been able to recognize individuals referrable to the race _macrocristatus_. Firschein and Smith (1957:219) described _macrocristatus_ from the mountains of eastern Oaxaca and referred to it specimens from the Gulf lowlands of northern Chiapas. None of the present material shows the hypertrophied cranial crests supposedly characteristic of _macroaristatus_, nor do specimens from the isthmus resemble the population in the Grijalva Valley being described by L. C. Stuart, who will discuss the variation in, and the validity of, the named populations of _valliceps_. Five specimens from San Lorenzo, Veracruz (USNM 123516-20), were identified as _Bufo cristatus_ by Smith (1947:408). Firschein (1950:83) redefined the _cristatus_ group of _Bufo_ and assigned these specimens to _valliceps_.