Chapter II: Part 2

Four species occur on the Gulf lowlands to the east and to the west of the isthmus, but on the Pacific lowlands they occur only to the east; this group includes _Bufo valliceps_, _Eleutherodactylus rhodopis_, _Phrynohyas modesta_, and _Phrynohyas spilomma_. Three species live to the east and to the west of the isthmus on the Pacific lowlands, but only to the west on the Gulf lowlands; these include _Eleutherodactylus rugulosus_, _Microbatrachylus pygmaeus_, and _Gastrophryne usta_.

Six species that cross the isthmus live on the humid Gulf lowlands and on the humid lowlands of Chiapas and Guatemala, but not on the semi-arid Plains of Tehuantepec; these include _Bolitoglossa occidentalis_, _Eleutherodactylus rhodopis_, _Microbatrachylus pygmaeus_, _Phrynohyas modesta_, _Phrynohyas spilomma_, and _Rana palmipes_. Of these, _Microbatrachylus pygmaeus_ also occurs in scattered humid environments to the west of the isthmus on the Pacific lowlands.

Two species are endemic to the isthmian region. _Bolitoglossa veracrucis_ is known only from the humid northern slopes of the isthmus. _Hylella sumichrasti_ occurs on the Pacific slopes of the isthmus and extends to the east into western Chiapas.

In analyzing the distribution of the amphibians with respect to those that are restricted to either the Pacific or Gulf lowlands or those that cross the continental divide in the isthmus, we find that 25 per cent of the species are restricted to the Gulf lowlands, 17 per cent are restricted to the Pacific lowlands, and 53 per cent cross the isthmus. In analyzing the distribution patterns with respect to those that extend across the isthmus of Tehuantepec from east to west, we find that 14 per cent of the species do not extend east of the isthmus into Central America and that 19 per cent do not range west of the isthmus into Mexico proper; 61 per cent of the species range to the east and to the west of the isthmus. Of the 36 species of amphibians inhabiting the isthmus only nine species (25 per cent) range across the isthmus, that is, occur on the Gulf and Pacific lowlands, and also range to the east and to the west of the isthmus. To these wide-ranging species the diversified environments of the isthmus do not present a barrier to distribution. The other 27 species (75 per cent) either do not cross the isthmus from east to west or from north to south; thus, probably in one way or another the isthmus presents a barrier to their distribution.

THE AMPHIBIAN FAUNA OF THE FOOTHILLS AND ADJACENT HIGHLANDS

To amphibians inhabiting the foothills and mountains of southern Mexico and northern Central America, the isthmus presents a great barrier to dispersal. For example, salamanders of the genus _Thorius_, the _mexicanus_ and _augusti_ groups of the genus _Eleutherodactylus_, the _bistincta_ group of the genus _Hyla_, and the genus _Tomodactylus_ occur on the Mexican Plateau and southward into the mountains of Oaxaca. Nevertheless, no members of these groups are present in the Guatemalan-Chiapan Highlands. The genera _Chiropterotriton_, _Magnadigita_, _Pseudoeurycea_, and _Ptychohyla_, as well as the _eximia_ group of _Hyla_ are represented by different species in the Guatemalan-Chiapan Highlands than in the mountains of Mexico on the other side of the isthmus. Several species of _Plectrohyla_ occur in the Guatemalan-Chiapan Highlands, but none is known from the Mexican Highlands, although one species occurs in the Tuxtlas.

Living in the humid forests of the foothills are salamanders of the genus _Lineatriton_, frogs of the _spatulatus_ group of _Eleutherodactylus_, _Anotheca coronata_, _Hyla miotympanum_, and _Phyllomedusa moreleti_. All of these occur in the foothills of the Sierra Madre Oriental in eastern Mexico and in Los Tuxtlas. _Lineatriton_, _Hyla miotympanum_, and the _spatulatus_ group of _Eleutherodactylus_ do not occur in the foothills of the Guatemalan-Chiapan Highlands; those amphibians reach the end of their ranges at the isthmus. _Phyllomedusa moreleti_ and _Anotheca coronata_ are found in the northern foothills of the Guatemalan-Chiapan Highlands, and _Phyllomedusa moreleti_ is found in the foothills on the Pacific slopes of the Chiapan Highlands.

Although the above analysis is not so detailed as that of the lowland inhabitants, it does show that all of the genera and species of amphibians known to inhabit the foothills and highlands adjacent to the isthmus, only two species of amphibians cross the isthmus from one highland mass to the other. Thus, it is evident that the Isthmus of Tehuantepec presents a great barrier to dispersal of these groups of amphibians.

ESTABLISHMENT OF PRESENT PATTERNS OF DISTRIBUTION

From the foregoing analysis of geographical and ecological distribution in the Isthmus of Tehuantepec we may strive for an interpretation of the events that led to the establishment of patterns of distribution displayed not only by the amphibians, but other terrestrial vertebrates as well. The thesis that I am proposing below is based on the premise that in southern Mexico and northern Central America climatic fluctuation during the Pleistocene was of sufficient magnitude to cause vegetational shifts, both vertically and latitudinally, resulting in the establishment of alternating continuous and discontinuous lowland and highland environments, although this climatic fluctuation was not so great as to eliminate tropical lowland environments from the region. I feel that the present patterns of distribution of the amphibians in the Isthmus of Tehuantepec may be explained on this premise.

Many authors dealing with the herpetofauna of Middle America have followed Schuchert's (1935) suggestion of a seaway in the isthmus during the Cenozoic. Thus, Burt (1931), Duellman (1956, 1958a), Gloyd (1940), Oliver (1948), Smith and Laufe (1946), and Stuart (1941) employed the presence of a seaway to explain distribution and speciation in various genera. Durham, Arellano, and Peck (1952), Olson and McGrew (1941), and Stirton (1954) have provided geological evidence that there probably was no Cenozoic seaway in the Isthmus of Tehuantepec. Even if there were a seaway in the Pliocene or Miocene (the dating of this possible seaway is open to question), its presence is not necessary to explain the present patterns of distribution in the isthmus.

In recent years the study of natural biotic environments, palynology, and Pleistocene chronology in Middle America has produced a wealth of data, which although still fragmentary begins to form a picture of past climatic events in that part of the world. Sedimentary studies by Hutchinson, Patrick, and Deevey (1956) and Sears, Foreman, and Clisby (1955) have provided evidence of drastic climatic shifts in Mexico during the Pleistocene. Further evidence of bioclimatic fluctuation is provided by Martin and Harrell (1957) and Martin (1958); the latter has suggested that there was a displacement of the tropical zones in southern Mexico and northern Central America by as much as 3000 feet during the glacial maximum. Much of the evidence of such drastic vertical shifts in environments is based on the presence of Pleistocene montane glaciers on Mexican volcanoes (White, 1956) and Chirripo in Costa Rica (Weyl, 1955). Dorf (1959) supports this idea of drastic climatic change.

In his studies of the avifauna of Mexico and Guatemala Griscom (1932 and 1950) made an important issue of the continuity of the bird fauna in what he called the Subtropical Life-zone, which essentially consists of cloud forest, a widespread, but discontinuous, habitat on the Gulf (windward) slopes of the Mexican and Central American highlands at elevations between 1000 and 2000 meters. To account for this apparent uniformity in the avifauna Griscom hypothesized a continuity of cloud forest environment in the Pleistocene; this would result in the depression of cloud forests to the coastal lowlands and the displacement of tropical lowland environments far to the south in Central America. Stuart (1951) objected to this displacement of lowland tropical rainforest; he stated that a descent to sea level of a subtropical zone would have brought about either widespread extermination of the tropical fauna or acclimatization of that fauna to subtropical conditions.

Although palynological studies and some faunal studies of subtropical and temperate animals suggest a drastic climatic fluctuation that might have eliminated tropical environments in southern Mexico and northern Central America, there is much biological evidence indicating the existence of tropical environments in this region even during the glacial maximum. Especially significant is the diversity of species inhabiting the present tropical environments; many of these have differentiated from related taxa to the south.

In the Pleistocene, climate fluctuated and vegetation shifted correspondingly in southern Mexico and northern Central America. Most of the palynological studies and many studies of Pleistocene chronology deal with montane regions, either the Mexican Plateau or the mountains rising from the plateau. No such studies have been made in lowland tropical environments. During glacial advances the tropical lowland environments in Mexico probably were not eliminated, for the great diversity of animals in these environments supports the hypothesis that they have been in existence for some time, although periodically they may have been discontinuous.

In order to understand the nature of bioclimatological events in the Pleistocene in lowland tropical environments of southern Mexico, certain factors that are of little importance in the interpretation of Pleistocene chronology in the highlands must be considered. These factors are: 1) climatic moderation by oceans, 2) fluctuation in sea level, and 3) fluctuation in level of the water table as affected by sea level.

It is well-known that large bodies of water moderate the temperature on adjacent land. Furthermore, it is known that faunas of marine invertebrates shifted latitudinally in the Pleistocene; Trask, Phleger, and Stetson (1947) recorded cold-water Foraminifera then as far south as the Sigsbee Deep in the middle of the Gulf of Mexico. Large bodies of warm water, such as the Gulf of Mexico, Caribbean Sea, and Pacific Ocean of today, probably were not sufficiently cooled at the time of glacial advance to affect greatly the temperature of the winds blowing across them. Even if these bodies of water were somewhat cooler than now, the prevailing winds blowing from them onto the lowlands of Mexico and northern Central America would have aided in maintaining relatively high temperatures there. These warm winds probably counteracted the cooling effect of glaciation in the lowlands and thereby maintained tropical conditions near the seas.

Although no adequate studies of Pleistocene beach lines have been made in southern Mexico, such information is available for peninsular Florida on the other side of the Gulf of Mexico (Cooke, 1945). Fluctuation in sea level in the Pleistocene has been used by Hubbell (1954), Goin (1958), and Duellman and Schwartz (1958) to explain present patterns of distribution of animals in Florida. If Cooke's interpretations can be applied to the western side of the Gulf of Mexico, even generally, it would be supposed that sea level varied from about 300 feet lower than at present during the Illinoian Glacial Period to about 275 feet higher than at present during the Aftonian Interglacial Period. Lowering of sea level would expand the lowlands in the isthmus; rising sea level would restrict them, leaving only the central ridges and many islands in the isthmus, but never forming a seaway between the Gulf of Mexico and the Pacific Ocean.

Probably the level of the water table in the coastal lowlands and the gradients of the streams in the lowlands and foothills was closely correlated with fluctuation in sea level. If sea level fluctuated as much as 575 feet in the Pleistocene, changes in the level of the water table must have been of considerable magnitude.

During times of glacial advances the lowlands of the isthmus probably were more extensive and had more semi-arid tropical environments than at present, with patches of rainforest existing in sheltered valleys along the major streams. In the course of bio-climatic fluctuation the semi-arid environments (scrub forest and/or savanna) were continuous at times from the Pacific lowlands across the isthmus to the Gulf lowlands. At those times such typical inhabitants of the semi-arid environments as _Rhinophrynus dorsalis_, _Engystomops pustulosus_, and _Hyla staufferi_ could have made their way across the isthmus. At times of most extensive glaciation, such as the Illinoian, temperatures in the isthmus probably were low enough to permit the growth of pine-oak forest and cloud forest continuously across the central ridges from the Mexican to the Chiapan-Guatemalan highlands. At those times such highland members of the fauna as _Chiropterotriton_, _Pseudoeurycea_, _Magnadigita_, and the _eximia_ group of _Hyla_ could have crossed the isthmus. During Wisconsin time, climate probably fluctuated less than during previous glaciations; probably no montane environments, except cloud forest, were represented in the isthmus during the Wisconsin. Even at this relatively late date such animals as _Lineatriton lineola_, _Anotheca coronata_, and _Phyllomedusa moreleti_ could have crossed the isthmus.

During the interglacial periods, which in the isthmian region were characterized by warmer temperatures, higher sea level and consequently more restricted areas of lowlands, and possibly more rainfall than in the glacial periods, the continuity of pine-oak forest and cloud forest from east to west across the isthmus was interrupted. Probably, too, the semi-arid environments were restricted, and the rainforests were more widespread. At those times animals now inhabiting the rainforests of the Gulf lowlands and those inhabiting the Pacific lowlands of Chiapas and Guatemala could have crossed the isthmus. In this group are species such as _Bolitoglossa occidentalis_, _Eleutherodactylus rhodopis_, _Microbatrachylus pygmaeus_, and _Rana palmipes_.

The amount of differentiation in isolated populations of amphibians in southern Mexico and northern Central America gives some idea of relative lengths of time of isolation from related populations. Those populations inhabiting high mountain environments on either side of the isthmus are specifically distinct. Some populations inhabiting cloud forests lower on the mountains are specifically distinct from related populations on the other side of the isthmus; between others there is no recognizable differentiation. Even though many populations are isolated from other populations of the same species in the lowlands of the isthmus, there is no apparent speciation. This indicates that the lowland environments and their inhabitants have been isolated from one another for a shorter time than have the highland environments and their inhabitants.

ACCOUNTS OF SPECIES

For each species of amphibian known to occur in the lowlands of the Isthmus of Tehuantepec, localities where one or more specimens were collected are listed, and variation, ecology, and life histories are discussed. A total of 2833 specimens has been examined for the purposes of this study. Individual specimens cited in the text are listed with catalogue numbers and abbreviations of the name of the museum, as follows:

AMNH American Museum of Natural History
KU University of Kansas Museum of Natural History
MCZ Museum of Comparative Zoology, Harvard College
UIMNH University of Illinois Museum of Natural History
UMMZ University of Michigan Museum of Zoology
USNM United States National Museum

=Gymnopis mexicanus mexicanus= Dumeril and Bibron

_Oaxaca_: El Barrio (3); Matias Romero; Tehuantepec (2).
_Veracruz_: Cosamaloapan; Cuatotolapam (2).

The two specimens from Cuatotolapam were collected by Ruthven in an area of mixed savanna and forest. The three specimens (USNM 30535-7) listed above from El Barrio were collected by Sumichrast; possibly they came from another locality. The city of Tehuantepec is divided into seven districts called "barrios." The two specimens listed from Tehuantepec (MCZ 1604) merely bear the data "Tehuantepec, Mexico." They may have come from the town, the district, or from anywhere in the isthmus. The specimen from Matias Romero has 109 primary and 67 secondary annuli, a length of 400 mm., and a diameter of 19 mm.; the one from Cosamaloapan has 106 primary and 58 secondary annuli, a length of 397 mm., and a diameter of 19 mm. Data on the other specimens were recorded by Dunn (1942:475).

=Bolitoglossa occidentalis= Taylor

_Oaxaca_: Rio Sarabia (2); Ubero. _Veracruz_: La Oaxaquena;
14 km. E of Suchil.

The specimens from Oaxaca are only tentatively assigned to _occidentalis_. All are immature and lack maxillary teeth. Taylor (1941:147) stated that the maxillary teeth are absent in young _occidentalis_. One from Rio Sarabia is a male with a body-length of 29 mm. and a tail-length of 22 mm. The dorsum is reddish brown streaked with dark gray; the venter is dark gray. Two small individuals (one from Sarabia and one from Ubero) have body-lengths of 19 and 21 mm. and tail-lengths of 10.5 and 11 mm. In life they were pale yellowish tan above with a brown triangular mark on the occiput, but with no middorsal stripe. Both were found in the axils of elephant ear plants (_Xanthosoma_).

This species has been noted by Goodnight and Goodnight (1956:146) on the Atlantic lowlands at Palenque, Chiapas, and by Shannon and Werler (1955:362) at several localities in Los Tuxtlas, Veracruz. I have collected it at Vista Hermosa on the eastern slopes of the Sierra Madre Oriental above Tuxtepec in northern Oaxaca. Both _B. occidentalis_ and _B. rufescens_ have been reported from Palenque, Chiapas (Taylor and Smith, 1945:547). Reexamination of specimens from northern Chiapas and Tabasco is needed to verify the sympatric occurrence of these two similar species.

=Bolitoglossa platydactyla= Tschudi

_Oaxaca_: La Oaxaquena; Tolosita (2). _Veracruz_: Acayucan;
Cuatotolapam; 25 km. ESE of Jesus Carranza; 14 km. E of
Suchil; 2.7 km. N of Tula.

Known only from the Gulf lowlands in the isthmian region, this species has been taken in a variety of habitats within the humid forest area: under outer leaves of banana plants, under a rock along a stream, under a log in a plowed field, and on a reed in a pond at night. Three adult males have an average snout-vent length of 44 mm. and a tail-length of 41 mm. In life the color of the dorsum varied from orange-yellow to orange-tan, usually being more orange on the tail. The iris was a reddish orange.

=Bolitoglossa veracrucis= Taylor

_Veracruz_: 35 km. SE of Jesus Carranza (21).

This species is known only from the type series collected at night on a limestone cliff by Walter W. Dalquest. If this salamander is restricted to this type of habitat, it should be found in the region of extensive limestone outcroppings in northern Chiapas and southern Tabasco.

=Rhinophrynus dorsalis= Dumeril and Bibron

_Oaxaca_: Ixtepec; Limon; Salina Cruz (18); Tehuantepec
(57); Tuxtepec (3). _Veracruz_: Amatitlan (3); Cosamaloapan
(5); Novillero (2); San Lorenzo.

This species inhabits the scrub forests of the Pacific coastal plain and the savannas in southern Veracruz; apparently it does not occur in rainforest. Consequently, its distribution in the isthmus is discontinuous.

PLATE 1

PLATE 2

PLATE 3

PLATE 4

PLATE 5

PLATE 6

PLATE 7

PLATE 8

Breeding congregations were found after heavy rains at Tehuantepec on July 5, 1956, at Cosamaloapan, Novillero, and Amatitlan on July 26, 1956, and at Salina Cruz on July 6, 1958. The call is a long "worrp" made while the male is floating on the surface of the pond. The small heads, small limbs, and greatly inflated bodies cause the calling males to resemble miniature caricature balloons (Pl. 6, fig. 1). Amplexus is inguinal. These toads are notably wary, even when calling. Often the beam of a flashlight or the slightest disturbance of the water will cause the males to stop calling. The body is deflated with one last nauseous note, and the frog sinks beneath the surface of the water and swims away with short slow kicks of the hind feet.

=Bufo canaliferus= Cope

_Oaxaca_: Chivela; Salina Cruz; Santa Efigenia; Tapanatepec
(6); Tehuantepec (10); Zanatepec (4).

This small toad apparently is restricted to the Pacific lowlands from the Isthmus of Tehuantepec eastward to Guatemala. At Zanatepec on July 13, 1956, males were calling from a flooded field bordered by scrub forest. The call is a rather loud nasal racket. Living individuals vary greatly in coloration. Some have yellowish tan flanks and dorsum and an orange middorsal stripe; others have a pale red dorsum, yellow flanks, and a cream middorsal stripe (Pl. 6, fig. 2).

=Bufo coccifer= Cope

_Oaxaca_: Juchitan (5); Tehuantepec.

It is with some degree of hesitancy that these toads are referred to the species _coccifer_. Although these and other specimens from Guerrero and Michoacan display no striking differences from specimens from Costa Rica, Nicaragua, and southeastern Guatemala, the ranges of the populations are separated by a broad hiatus in Chiapas and Guatemala. Possibly this species has utilized the sub-humid corridor through northern Central America (Stuart, 1954) and subsequently disappeared from the corridor in Guatemala and Chiapas. Specimens of a _coccifer_-like toad collected by Stuart in the vicinity of Jacaltenango, Departamento Huehuetenango, Guatemala, are much larger than either the Central American or Mexican specimens of _coccifer_. A final commitment on the systematic status must await a thorough study of this group of toads.

Males of this species were calling from a grassy rain-pool in open scrub forest at the edge of Juchitan on July 6, 1956. The call is a low "whirrr." The calling males were sitting in the shallow water at the edge of pond, where they were hidden by the grass. None was observed in open water, as is characteristic of calling males of _Bufo canaliferus_ and _marmoreus_.

=Bufo marinus= Linnaeus

_Oaxaca_: Agua Caliente; Guichicovi (3); Mixtequilla;
Tolosita (6); Tehuantepec (37); Tuxtepec; Union Hidalgo.
_Veracruz_: Ciudad Aleman (4); Cosamaloapan; Cuatotolapam
(19); 20 km. SE of Jesus Carranza (4); 38 km. SE of Jesus
Carranza (10); 20 km. NE of Jesus Carranza (4); Novillero.

This large toad is abundant throughout the lowlands of the isthmus. The loud rattling call of males was heard on rainy nights throughout the summer. In March, 1956, several adults were found in a small cave back of a spring at Agua Caliente.

=Bufo marmoreus= Wiegmann

_Oaxaca_: Cerro San Pedro (2); Chivela (5); Escurano (3);
Juchitan; Salina Cruz (101); Santa Lucia (2); 12 km. S of
Santiago Chivela (11); Santo Domingo; Tapanatepec;
Tehuantepec (100); Tequisistlan. _Veracruz_: Alvarado;
Coatzacoalcos.

This toad is abundant on the Pacific lowlands, where it inhabits both open and dense scrub forest. On the Gulf lowlands its distribution seems to be limited to xeric coastal habitats. Aside from the specimens from Alvarado and Coatzacoalcos, it is known in Veracruz only from Boca del Rio (Langebartel and Smith, 1959:27).

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_.

=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 relationship. _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); Minatitlan; 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 shines 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 masses were along the bank of a pond near Tehuantepec; one large composite egg mass 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 labialis= 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).

Although _Leptodactylus labialis_ does not appear to be so abundant as _Leptodactylus melanonotus_, the former was found throughout the lowlands of the isthmus. In the dry season individuals were found along streams, and in the rainy season breeding congregations were found in rain pools, marshes, ponds, and even small puddles. The call is a slow "wort, wort, wort." Males call beneath the water and from beneath rocks and from holes in the ground. The average snout-vent length of eight adult males is 37.2 mm. A completely metamorphosed juvenile obtained at Hueyapan on July 24, 1956, has a snout-vent length of 11 mm.

=Leptodactylus melanonotus= Hallowell

_Oaxaca_: Agua Caliente (25); Cerro Arenal (2); Cerro
Quiengola (3); Cerro San Pedro (3); Chivela (2); Coyol;
Juchitan; Matias Romero (11); Mixtequilla (2); Papaloapan
(2); Salazar (9); Salina Cruz; 11 km. S of Santiago Chivela;
Tapanatepec (17); Tehuantepec (176); Tolosita; Union
Hidalgo; 27 km. W of Zanatepec (6). _Veracruz_: Acayucan;
Cuatotolapam (9); Cosoleacaque; 20 km. ENE of Jesus Carranza
(2); 20 km. SE of Minatitlan (2); Novillero; San Lorenzo
(6).

This frog is abundant throughout the lowlands of the isthmus, where in the dry season individuals were found along streams and beneath rocks at a spring seepage. In the rainy season males were calling from nearly every bit of standing water. The call is a soft clicking sound resembling that made by striking two small stones together. The average snout-vent length of ten adult males is 41.8 mm. There is considerable variation in the extent of the yellowish brown glandular areas on the belly. Some have none, whereas others have a broad area on the chest, a band along the flanks, and a thin band across the lower abdomen. Individuals collected in the dry season vary in the same fashion as do those collected in the rainy season, at which time they were breeding. The glands are equally well-developed in adults of both sexes, and were present in some juveniles with snout-vent lengths of less than 20 mm. Apparently the development of the glands is not associated with maturity, sex, or size.

=Diaglena reticulata= Taylor

_Oaxaca_: Cerro Arenal; Chivela; Salina Cruz (26); San
Antonio (3); Tehuantepec (2); 8.6 km. W of Tehuantepec (11);
Zarzamora.

Breeding congregations of this rare frog were found 8.6 kilometers west of Tehuantepec on July 5, 1956, and at Salina Cruz on July 6, 1958. Both choruses took place immediately after torrential rains. In both instances the frogs were in and about open muddy pools in the scrub forest (Pl. 5, fig. 2); males called from the bank near the water, and clasping pairs were found only on land (Pl. 8, figs. 1-2). The call is a loud, nasal "braaa," two to three seconds in duration. Amplexus is axillary.

The dorsal ground color is light yellowish green tending towards olive on the head and fading to yellow on the flanks. The ventral surfaces, including the vocal sac, are white; the iris is golden and flecked with black. The present series agrees well with the description of _reticulata_ (based on two specimens) given by Taylor (1942:60). A detailed analysis of variation, comparison with related species, and descriptions of tadpoles are reserved for a future report.

=Hyla baudini= Dumeril and Bibron

_Oaxaca_: Bisilana; Cerro Quiengola (2); Cerro San Pedro;
Coyol; Matias Romero (12); Mixtequilla; Rio Sarabia (7);
Salazar; San Antonio; 11 km. S of Santiago Chivela; Santo
Domingo (3); Tapanatepec (2); Tehuantepec (23); Tolosita.
_Veracruz_: Acayucan; Amatitlan; Ciudad Aleman (3);
Cosamaloapan (2); Cuatotolapam (15); 10 km. SE of Hueyapan;
20 km. S of Jesus Carranza; 38 km. S of Jesus Carranza (2);
20 km. ENE of Jesus Carranza (4); La Oaxaquena (2);
Minatitlan (2); Naranja (3); Novillero (9); Rio de las
Playas (2); San Lorenzo (5); Tapalapan (2).

Commonly found on both sides of the isthmus, this large tree frog nearly always is associated with trees; it is not found in the savannas, although it breeds in savannas adjacent to rainforest. It appears to be somewhat more abundant in scrub forest than in rainforest. In the daytime individuals were found under the outer sheaths of banana plants, in the axils of leaves of elephant ears (_Xanthosoma_), in cavities in trees, and on shaded limbs in the forest. Recently metamorphosed individuals having snout-vent lengths slightly more than 20 mm. were found in the latter part of July.

=Hyla ebraccata= Cope

_Oaxaca_: Donaji (17); 43 km. N of Matias Romero (27);
Sarabia (6); Tolosita (3); Ubero (17). _Veracruz_: Aquilera.

This small species was found only in forested areas, where calling males were on bushes and trees around rain pools. The call is a harsh squawk repeated at intervals of 15 to 20 seconds, followed by a minute or more of silence, and then repeated. Clasping pairs were found on bushes and in the water.

The dorsum bears a dark chocolate brown hour glass-shaped mark, which in some individuals is broken into a large mark posteriorly and a smaller triangular one on the head and nape. The dorsal ground color varies from pale cream or ivory to yellow or tan. The intensity of the dorsal pigmentation is subject to rather rapid change. The flanks, hands, and anterior part of the venter are lemon yellow; the feet, thighs, and posterior part of the venter are golden yellow. The dorsal surface of the shank is yellow to tan with chocolate brown bars or spots; the heel is pale yellow. There is a dark brown bar in the loreal region and a dark brown bar extending posteriorly from the eye to a point above the insertion of the forelimb. The iris is a copper color. The toes are completely webbed; the fingers, one-third webbed. There is a small axillary web that is evident when the forelimbs are at right angles to the body. Twenty males have an average snout-vent length of 28.1 mm.; three females, 35.3 mm. There are no nuptial tuberosities on the pollex of breeding males.

This species has been collected at Coyame and Catemaco in Los Tuxtlas and at various localities in Tabasco; it apparently ranges eastward from southern Veracruz, Mexico, in humid forests to El Peten, Guatemala.

=Hyla loquax= Gaige and Stuart

_Oaxaca_: Donaji (7); 43 km. N of Matias Romero (21).
_Veracruz_: 19 km. N of Acayucan (4); Aquilera (3); 8 km. SW
of Coatzacoalcos (36); Cuototolapam (11); Naranja (13); San
Lorenzo (8).

In the isthmus this species is known only from the humid forests of the Gulf lowlands; it is also known from Boca del Rio, Veracruz, and from Teapa and Villa Hermosa, Tabasco.

Calling males were found on aquatic plants above the water in deep ponds in the forest where it was necessary for the collector to wade waist-deep in water to obtain them. The call is a loud "hah-onk." Individuals, when active at night, are yellowish tan above with light olive green spots. The flanks, belly, and vocal sac are yellow, and the anterior and posterior surfaces of the thighs and webbing of the feet are bright orange-red or tomato red. Individuals found during the day are grayish brown with olive markings or reddish brown with black markings. Sleeping individuals are ivory-gray with faint gray markings. The iris is a bright copper color. Fifteen adult males have an average snout-vent length of 41.7 mm.; they have no horny nuptial pads on the pollex.

The relationships of this species are with _Hyla rickardsi_ Taylor, a species known only from the foothills of the Sierra Madre Oriental in the states of Puebla and Veracruz. The distinguishing characteristics of these species are given in Table 1. Living individuals may be distinguished immediately by the flash colors on the thighs--red in _loquax_ and yellow in _rickardsi_. The calls of the two species are distinctly different; that of _rickardsi_ is a high-pitched, loud rattle continued for several seconds, notably different from the goose-like honk of _loquax_.

TABLE 1.--COMPARISON OF CERTAIN CHARACTERS IN HYLA LOQUAX AND HYLA RICKARDSI

=================================+================+==================== CHARACTER | _loquax_ | _rickardsi_ ---------------------------------+----------------+-------------------- Toe webbing | Full | Three-fourths | | Finger webbing | Three-fourths | One-half | | Average snout-vent length (Male) | 41.7 mm. | 37.4 mm. | | Tympanum/eye (Male) | 63.2% | 55.8% | | Dorsal leg pattern | Barred | Unmarked | | Tarsal fold | Tubercular | Absent | | Tarsal stripe | Absent or | Broad, indistinct, | indistinct | or absent | | Dorsolateral stripe | Absent | Present | | Light line over anus | Broad | Narrow | | Flash colors | Red | Yellow | | Iris color | Copper | Bronze ---------------------------------+----------------+--------------------

The three specimens from San Lorenzo, Veracruz (USNM 123513-5), were identified as _Hyla rickardsi_ by Smith (1947:409). The flash colors have faded in preservative, and so are of no aid in identifying these specimens. Two are adult females with snout-vent lengths of 35 and 39 mm. In possessing a relatively large tympanum and barred thighs, and in lacking a dorsolateral stripe they are typical of _loquax_, but in the amount of webbing on the hands and feet, broad tarsal stripe, and narrow anal stripe they are like _rickardsi_. The third specimen, a juvenile, has a snout-vent length of 25 mm. In coloration it resembles the adults; it has more distinct bars on the limbs. On the basis of geography these specimens should be _loquax_, for the closest known record of _rickardsi_ is more than 200 kilometers to the northwest, whereas _loquax_ is known from several localities around San Lorenzo.

Shannon and Werler (1955:383) described _Hyla axillamembrana_ from the lower southern slopes of Los Tuxtlas. The unique type is a small male (27 mm. snout-vent). I have examined the type and find no great differences between it and small specimens of _loquax_. It is not possible to determine the color of the thighs, nor was this information given in the description. _Hyla axillamembrana_ is here considered to be a synonym of _Hyla loquax_.

=Hyla microcephala martini= Smith

_Oaxaca_: Donaji (15); 43 km. N of Matias Romero (19); Rio
Sarabia (2); Sarabia (11); Tolosita. _Veracruz_: Acayucan
(17); Alvarado (41); Aquilera (21); 8 km. SW of
Coatzacoalcos (10); Cosoleacaque (26); 10 km. SE of
Hueyapan; Naranja (3); Novillero.

This frog is abundant in the Gulf lowlands of the isthmus, where large breeding congregations were found in grassy ponds on the savannas and in openings in the forest. Most frequently males were calling from grasses and reeds in the ponds; many individuals were perched precariously on thin blades as high as one meter above the water. The call is a series of low squeaks.

Individuals found at night were pale yellow above with light brown lines arranged in an irregular pattern on the back, but often forming a cross or an X-shaped mark in the scapular region. There is a brown stripe from the nostril to the eye and thence to the groin. Anteriorly this stripe is bordered above by a thin white or cream-colored line. Numerous small brown flecks are scattered on the back and dorsal surface of the shank. In most specimens there are thin transverse brown bars on the shank. The thighs and undersides of the limbs are golden yellow; the belly and vocal sac are lemon yellow. The iris is yellowish brown. During the day individuals assume a pale reddish tan ground color with darker brown markings. Twenty-five adult males from Alvarado have an average snout-vent length of 24.1 mm.

=Hyla picta= Guenther

_Oaxaca_: Donaji (8); Sarabia (11); Tolosita (15); Ubero
(6). _Veracruz_: 19 km. N of Acayucan (4); Alvarado (5);
Aquilera; 8 km. SW of Coatzacoalcos; 10 km. SE of Hueyapan
(7); Lerdo de Tejada; Tula (3).

Widespread in the forests, scrub, and savannas on the Gulf lowlands of the isthmus, these frogs were found breeding at numerous localities. Males call from grasses and bushes growing in and about ponds. The call is a high-pitched insect-like trill. At night these frogs are pale yellow above; they change to light grayish tan during the day. A dark stripe extends from the nostril to the eye and thence posteriorly to a point between the axilla and groin. Above this dark stripe is a broader white stripe. Scattered on the dorsum are brown flecks or spots; the shanks are marked with poorly-defined cross-bars. The thighs are deep yellow below and paler above with scattered dark flecks. The belly is white, and the vocal sac is yellow. The iris is golden. Twenty males have an average snout-vent length of 21.5 mm.; three females, 24.0 mm.

=Hyla robertmertensi= Taylor

_Oaxaca_: Tapanatepec (28); 7.5 km. NW of Tapanatepec (38);
7.2 km. WNW of Zanatepec (77).

This species was found in the isthmian region only on the Pacific lowlands at the southern base of the western part of the Sierra Madre de Chiapas. On July 13, 1956, many large choruses were discovered. The calling males were on reeds and thorn scrub in and at the edge of temporary ponds; the call is a cricket-like "creak-creack," quickly followed by a series of notes "creak-eek-eek-eek-eek."

At night the dorsal ground color is pale yellow; this changes to pinkish buff during the day. There is a grayish or brown dark stripe from the nostril to the eye; the stripe continues to the groin. This dark stripe is bordered above by a narrow white stripe. The belly is white, and the vocal sac is yellow. The iris is dull reddish brown. Twenty-five males have an average snout-vent length of 24.7 mm.

=Hyla staufferi= Cope

_Oaxaca_: Chivela; Huilotepec (5); Juchitan (4); Matias
Romero (4); 25 km. N of Matias Romero; Mixtequilla (4); Rio
Sarabia (11); 11 km. S of Santiago Chivela; Sarabia (3);
Tapanatepec (67); Tehuantepec (66); Tolosita (2); Ubero;
Union Hidalgo; Zanatepec (6). _Veracruz_: Acayucan (7);
Alvarado (3); Amatitlan; Aquilera; Ciudad Aleman (3); 8 km.
SW of Coatzacoalcos (9); Cosamaloapan (4); Cosoleacaque (8);
10 km. SE of Hueyapan; Lerdo de Tejada; Novillero (6); Tula
(2).

This is the only species of small hylid that crosses the isthmus. Calling males were found in and about ponds on the savannas in southern Veracruz, in ponds in open forest in northern Oaxaca (not in forest pools), and in temporary pools in the scrub forest on the Pacific lowlands. Individuals usually called from bushes and reeds in or at the edge of ponds. The call is a short "braaa." Dates of breeding choruses indicate that by the time the other small species of hylids in the Gulf lowlands reach the peak of their breeding season, that of _H. staufferi_ is essentially over; no large breeding congregations were found in July. On July 8, 1956, two metamorphosing young were found clinging to blades of grass in a pond; they had snout-vent lengths of 8 and 9 mm. and tail stumps less than 3 mm. in length. Others were found on July 13 and 26. The juveniles are nearly unicolor olive green above and white below.

In life the adults vary greatly in color pattern. The dorsal ground color is yellowish tan to olive brown with olive brown or dark brown spots, some of which in certain individuals are connected to form longitudinal dark stripes. On the posterior surface of the thighs are small white flecks. The belly is white, and the vocal sac is a rich yellow. Twenty males have an average snout-vent length of 26.3 mm.; they have no horny nuptial pads. No noticeable differences in either color or body proportions were found between the populations on either side of the isthmus.

=Hylella sumichrasti= Brocchi

_Oaxaca_: Cerro Arenal (5); Cerro San Pedro (2); Escurano;
La Concepcion (41); Portillo Los Nanches (6); San Antonio
(16); 11 km. S of Santiago Chivela (18); Santa Lucia (7);
Tapanatepec (5); Tehuantepec (8); Tenango (49); Tres Cruces
(19).

With the exception of the series from 11 kilometers south of Santiago Chivela, most of these specimens were found in small arboreal bromeliads during the dry season. Males were found along a clear, shallow, rocky stream south of Santiago Chivela on July 6, 1956. The frogs were calling from bushes and rocks in and along the stream. When disturbed, they jumped into the water and floated downstream until they were able to hold onto a rock or other object. The call is a loud "bra-a-ah." In breeding individuals the dorsum is pale yellow; the belly is white, and the vocal sac is yellow. The iris is pale golden yellow. Eighteen males have an average snout-vent length of 25.2 mm. All have dark brown nuptial tuberosities on the pollex.

Certain diagnostic characters of this species as given by Taylor (1943a:50) and Taylor and Smith (1945:598) are in need of revision. _Hylella sumichrasti_ has been characterized as having no vocal sac, rarely having vomerine teeth, and as having a relatively smooth throat. The vocal sac in breeding males is quite evident; it is single, median, and when expanded, spherical. The openings into the vocal sac are narrow slits along the inner posterior border of the jaw rami. Of 151 specimens studied, 74 have vomerine ridges between the choanae, and 36 of these have one to three teeth on each ridge. The belly and undersurfaces of the thighs are granular; the throat is only somewhat less so. The granular condition may be correlated with breeding, for specimens obtained from bromeliads in the dry season had rather smooth throats. It seems that the vocal sac atrophys in the non-breeding season. These seasonal changes may account for the diagnoses given by Taylor (_op. cit._) and Taylor and Smith (_op. cit._); likewise, since many of the specimens obtained by Smith in the dry season were juveniles and subadults, the development of the vomerine ridges could not be diagnosed properly.

The range of this species encompasses the Pacific slopes of the Isthmus of Tehuantepec eastward to the upper Cintalapa Valley and vicinity of Tonala in western Chiapas. Priscilla Starrett collected tadpoles of _H. sumichrasti_ from a stream 19 km. N of Arriaga, Chiapas. These limited observations on the ecology of this frog suggest that it breeds in the fast-moving streams of the Pacific slopes, and that it seeks shelter in arboreal bromeliads during the dry season.

=Phrynohyas modesta= Taylor and Smith

_Oaxaca_: Tuxtepec. _Veracruz_: 20 km. S of Jesus Carranza;
20 km. ENE of Jesus Carranza (2); Minatitlan.

I have not collected this species in the isthmus. The locality records indicate that the range is discontinuous (Duellman, 1956:27). The species occurs on the humid Pacific slopes from south-central Chiapas eastward to El Salvador and on the humid Gulf lowlands from southern Veracruz eastward into Tabasco, but is unknown from the dry Pacific slopes and plains in the isthmus.