A Distributional Study of the Amphibians of the Isthmus of Tehuantepec, Mexico Part 6

_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; Amat.i.tlan; 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 a.s.signed these specimens to _valliceps_.

=Eleutherodactylus alfredi= Boulenger

_Oaxaca_: Tolosita (2). _Veracruz_: 35 km. SE of Jesus Carranza (6).

These specimens were collected in rainforest. Shreve (1957:247) pointed out the close resemblance between _E. alfredi_ and _E. conspicuus_ from Piedras Negras, Guatemala, and treated them as subspecies. Examination of the specimens from the isthmus, together with seven from central Veracruz and one from Teapa, Tabasco, suggests an even closer relations.h.i.+p. _Eleutherodactylus conspicuus_ was diagnosed by Taylor and Smith (1945:567) as differing from _alfredi_ "in lacking a tarsal fold, in having shorter hind legs with the tibiotarsal articulation reaching only to the nostril instead of beyond the tip of the snout; the vomerine teeth barely reach the posterior level of the choanae."

The specimen from Teapa has the vomerine teeth reaching to the posterior edge of the choanae; in the eight specimens from the isthmus the teeth reach the posterior edge of the choanae in two and to the middle of the choanae in six; in seven specimens from central Veracruz the teeth reach the posterior edge of the choanae in two and to the middle in five. The tibiotarsal articulation extends beyond the tip of the snout in the specimen from Teapa and in two from central Veracruz; in three specimens from the isthmus and in one from central Veracruz it extends only to the nostril; in the others it extends to the snout. The tarsal fold is absent in the specimen from Teapa, in three from the isthmus, and in all those from central Veracruz; it is weakly present in the others.

In the light of this evidence there seems to be little justification in recognizing two species or even two subspecies in this group.

Consequently, _Eleutherodactylus conspicuus_ Taylor and Smith (1945) is here placed in the synonymy of _Eleutherodactylus alfredi_ Boulenger (1898), a species with a range extending from Cuautlapan and Potrero Viejo in central Veracruz southward and eastward in forested habitats to western El Peten, Guatemala.

=Eleutherodactylus natator= Taylor

_Veracruz_: 35 km. SE of Jesus Carranza (3); 38 km. S of Jesus Carranza; 55 km. SE of Jesus Carranza.

The snout-vent length is 42.0 mm. in a male and averages 59.5 mm. in three adult females. The tarsal fold is low and extends about half the length of the tarsus; the first and second fingers are subequal in length; the tibiotarsal articulation extends beyond the tip of the snout. The patches of vomerine teeth lie between the posterior margins of the choanae. The throat and belly are immaculate, and the soles of the feet are dark. In the isthmus this species can be distinguished from _Eleutherodactylus rugulosus_ by less rugose skin on the dorsum and absence of dark ventral mottling.

The specimens reported here extend the known range of _natator_ eastward from Camotlan, Oaxaca; northward in Veracruz the species inhabits foothills as far north as Huatusco.

=Eleutherodactylus rhodopis= Cope

_Oaxaca_: 30 km. N of Matias Romero; Rio Sarabia (5); Tapanatepec (87); Tolosita (6); between Zanatepec and Tapanatepec. _Veracruz_: 25 km. SE of Jesus Carranza; 35 km.

SE of Jesus Carranza (2); 22 km. SSW of Jesus Carranza; 20 km. ENE of Jesus Carranza (7); Minat.i.tlan; Tapalapan (5).

For the purposes of the present study I am not recognizing _Eleutherodactylus beati_, _E. dorsoconcolor_, and _E. venustus_ as specifically, or even subspecifically distinct from the earlier named _E. rhodopis_. Probably these are mere color varieties of a single species.

In the dry season frogs of this species were in humid forests, where they were most frequently found along small streams and in ravines. The species is widespread in the Gulf lowlands, but does not occur on the Plains of Tehuantepec. It does inhabit the Pacific slopes on the foothills of the Sierra Madre de Chiapas, the western part of which extends into eastern Oaxaca near Tapanatepec.

=Eleutherodactylus rugulosus= Cope

_Oaxaca_: La Princesa (30); Modelo; Santa Lucia (10); Tapanatepec (26); Tehuantepec (6); Tres Cruces (8).

_Veracruz_: Tapalapan (5).

In addition to the specimens from the lowlands of the isthmus, for the purposes of the following discussion, I have included data on two specimens from the southern slopes of the Sierra del Sur in Oaxaca (Mirador and Chacalapa) and on several specimens from Los Tuxtlas in Veracruz (Los Chaneques, 67; Salto de Eyipantla, 35; and San Andres Tuxtla, 11).

Frogs of the _Eleutherodactylus rugulosus_ complex occur from southern Veracruz and Sinaloa southward through Central America. Taylor (1940:401) described _E. vocalis_ from Hacienda El Sabino, Michoacan; Taylor and Smith (1945:580) described _E. avocalis_ from Tres Cruces, Oaxaca. These have been considered as species distinct from _rugulosus_, which is known to occur in Veracruz, Guerrero, and Chiapas southward into Central America. Although the large number of specimens collected in the isthmus does not aid in defining the ranges of the taxa involved, these specimens do give some idea of the variation in certain characters in a given population.

In specimens from Los Tuxtlas the tarsal fold is well-developed and extends two-thirds to three-fourths the length of the tarsus; the tibiotarsal articulation reaches the nostril and sometimes slightly beyond the tip of the snout. In males the tympanum is nearly equal to the diameter of the eye; in females it is about one-half the diameter of the eye. The posterior surfaces of the thighs are dark brown or black with whitish or cream-colored spots, flecks, or irregular mottling. The tarsal fold is dark; the throat is pale in some individuals, but in most is mottled with dark brown or gray flecks.

Individuals from La Princesa near the continental divide in Oaxaca show the same variation in body proportions and development of the tarsal fold. The posterior surfaces of the thighs are dark brown indistinctly mottled with lighter brown. The throat is dark brown. Specimens from the Pacific slopes of Oaxaca, including the Plains of Tehuantepec, have dark brown thighs mottled with dusty cream. The tibiotarsal articulation extends slightly beyond the tip of the snout in all specimens. In males the tympanum is equal to about two-thirds the diameter of the eye. Duellman (1958b:6) discussed the variation in these characters in populations in Colima, Jalisco, and Michoacan.

Until the extent of variation of these characters is known throughout the range of _rugulosus_, the recognition of populations either as species or subspecies seems superfluous. Consequently, I have used the oldest name; this does not necessarily imply, however, that all populations of _rugulosus_ (_sensu lato_) are conspecific.

Of the 200 specimens examined, 15 have a middorsal stripe that is red or yellow. The iris varies from a copper to a dark golden color and s.h.i.+nes bright red at night. Many of the specimens are juveniles; these were collected in the dry season, at which time they were found beneath rocks along streams, in road culverts where there was some water, and in holes in banks and cliffs.

=Microbatrachylus pygmaeus= Taylor

_Oaxaca_: La Princesa (5); Matias Romero (9); Rio Sarabia (41); Tolosita (2). _Veracruz_: Jesus Carranza; 20 km. ENE of Jesus Carranza.

The specimens listed above vary widely in color patterns; some of the patterns are characteristic of certain named "species": _albolabris_, _imitator_, _lineatissimus_, and _minimus_. The large series from the Rio Sarabia contains all of the color patterns; this series was obtained in one small ravine in the rainforest. At least in the isthmian region, this species does not inhabit the Pacific slopes and lowlands.

=Syrrhophus leprus= Cope

_Oaxaca_: 33 km. N of Matias Romero; Santa Efigenia.

_Veracruz_: San Lorenzo.

Although the type locality is stated to be Santa Efigenia on the Pacific slopes of the Sierra Madre de Chiapas in eastern Oaxaca, the type specimen probably came from the northern slopes of the mountains.

All other known specimens are from the Gulf slopes and lowlands, and from several localities in Los Tuxtlas. Details concerning specimens from the isthmus and other parts of the range were given by Duellman (1958c:8).

Smith (1947:408) reported a specimen of _Syrrhophus verruculatus_ Peters from San Lorenzo, Veracruz; he stated that this specimen (USNM 123530) could not be _S. leprus_, because it had a gray belly, nor _S.

cystignathoides_, because of the dark and light dorsal coloration.

Firschein (1954:57) in his review of the species of _Syrrhophus_ in eastern Mexico referred the specimen to _S. cystignathoides_. The specimen is in poor condition. Nevertheless, specific determination is possible. Numerous specimens of _S. leprus_ from Los Tuxtlas have gray bellies; some have heavier pigmentation than the specimen from San Lorenzo. In preservative the dorsum is dark brown with lighter mottling. There is little doubt that the specimen from San Lorenzo is a _Syrrhophus leprus_, an abundant and widespread species in the humid Gulf lowlands of southern Mexico, and not _verruculatus_, if this is a valid species (see Firschein, _op. cit._:58), and not _cystignathoides_, a species known from San Luis Potosi southward to central Veracruz.

=Syrrhophus pipilans pipilans= Taylor

_Oaxaca_: Cerro Arenal; Cerro San Pedro; 6 km. N of Chivela; 14 km. W of Tehuantepec (2).

In the isthmian region this frog is known only from the Pacific slopes and the Plains of Tehuantepec. Males call from the ground and from trees to heights of about four meters. The call is a single, high, long "peep."

=Engystomops pustulosus= Cope

_Oaxaca_: Chivela; La Ventosa (3); Santo Domingo; Tapanatepec (14); Tehuantepec (61); Union Hidalgo (62).

_Veracruz_: Acayucan; Cuatotolapam (7); 10 km. SE of Hueyapan (11).

Large congregations were breeding at Tehuantepec on July 5, at Tapanatepec on July 13, and at Hueyapan on July 24, 1956. The frogs were breeding in open ponds in scrub forest and savanna; none was found in the rainforest. Males call while floating on the water (Pl. 7, fig.

1); the call is a soft "do-ing, do-ing" with a rising tone on the last note. Numerous individual egg ma.s.ses were along the bank of a pond near Tehuantepec; one large composite egg ma.s.s there had a surface area of about one square meter (Pl. 7, fig. 2). The large series from Union Hidalgo was obtained by digging specimens out of a dry sandy river bank in the dry season. Some of the individuals were buried to a depth of 25 centimeters.

In life individuals from the Pacific lowlands were dull brown and gray; those from Acayucan were dark chocolate brown to black with pink or red blotches, forearms, and dorsal stripe. Not all specimens from the Atlantic lowlands are so colored; individuals from Cordoba and Mirador, Veracruz, are like those from Tehuantepec.

=Leptodactylus l.a.b.i.alis= Cope

_Oaxaca_: Agua Caliente; Chivela (2); Matias Romero (12); 33 km. N of Matias Romero (4); Mixtequilla; Santa Efigenia; Tapanatepec; Tehuantepec (38); Tolosita (2); 33 km. W of Zanatepec (49). _Veracruz_: Acayucan (3); Ciudad Aleman; Cuatotolapam (10); Hueyapan; La Oaxaquena (4); 38 km. SE of Jesus Carranza; 20 km. ENE of Jesus Carranza; Novillero (3); San Lorenzo (2).