Part 3

Distribution.--Southern Sonora, México, and southern Texas throughout the Central and South American lowlands to Argentina. Also known from Hispaniola and Puerto Rico in the Greater Antilles and a few islands in the Lesser Antilles.

Entymology.--Greek (leptos + dactylus) meaning slender toes.

Genus ~Syrrhophus~ Cope, 1878

Type-species.--Syrrhophus marnockii Cope, 1878

Diagnosis and definition.--Small to medium sized frogs (18 to 40 mm. snout-vent) having slight to prominent digital expansions with transverse groove at tip of each digit; lumbo-inguinal and inguinal gland flattened, irregular in outline, not compact and oval; axillary glands present or not; plantar supernumerary tubercles numerous, more than eight, usually extending between metatarsal tubercles; tarsus lacking tubercles or folds; toes free or basally webbed; terminal phalanges T-shaped; sternum cartilaginous, lacking bony style; sphenethmoid not truncate anteriorly; nasals in contact medially; maxillary and quadratojugal in articular contact; anterior arm of squamosal not in contact with maxillary; dermal cranial elements not involved in integumentary-cranial co-ossification; prevomers large, usually lacking dentigerous processes and teeth; maxillary and premaxillary bones dentate; occipital condyles separated; development direct.

Composition.--Thirteen species; the species described as, or later referred to, Syrrhophus from Lower Central America and South America are Eleutherodactylus or Eupsophus.

Distribution.--Low to moderate elevations from Sinaloa, México, to Guatemala on the Pacific versant; from the Edwards and Stockton plateaus of Texas to British Honduras on the Caribbean versant.

Etymology.--Greek, emendation of syrrhaptos, meaning sewn together in reference to the united outer metatarsals.

Genus ~Tomodactylus~ Günther, 1900

Type-species.--Tomodactylus amulae Günther, 1900.

Diagnosis and definition.--Small frogs (20 to 35 mm. snout-vent length) having digital expansions or not, with transverse groove across tip of each digit; lumbo-inguinal gland prominently elevated, compact, oval, often patterned; axillary glands absent; plantar supernumerary tubercles numerous, more than eight, usually extending between metatarsal tubercles; tarsus lacking tubercles or folds; toes free; terminal phalanges T-shaped; sternum cartilaginous, lacking bony style; sphenethmoid not truncate anteriorly; nasals in contact medially; maxillary and quadratojugal in articular contact; anterior arm of squamosal not in contact with maxillary; dermal cranial elements not involved in integumentary-cranial co-ossification; prevomers large, usually bearing dentigerous processes; maxillary and premaxillary bones dentate; occipital condyles separated; development direct.

Composition.--Ten species.

Distribution.--The southern edge of the Mexican Plateau from Sinaloa to Veracruuz and onto the Oaxaca highlands and Sierra Madre del Sur.

Etymology.--Greek (tomis + dactylus) meaning knife toe; in reference to either the sharp subarticular tubercles or the unwebbed toes.

DISCUSSION

The preceding definitions only slightly alter the present generic limits of Mexican leptodactylids. Two species, previously regarded as Eleutherodactylus, are transferred to the new genus Hylactophryne. The arrangement of the species of Syrrhophus and Tomodactylus remains the same as concluded by Dixon (1957), Duellman (1958), and Firschein (1954) in their reviews of the genera.

Lumbo-inguinal glands are most prominent in the genera Pleurodema and Tomodactylus. Various nondescript glands are present in many genera, but none is so well developed as those of Pleurodema and Tomodactylus.

At least nine leptodactylid genera are either known or thought to be terrestrial breeders lacking a free-living tadpole stage (Eleutherodactylus, Euparkerella, Hylactophryne, Niceforonia, Noblella, Sminthillus, Syrrhophus, Tomodactylus and Trachyphrynus). Niceforonia and Trachyphrynus, and probably Hylactophryne, are not closely related to the other genera. Direct development probably is an adaptation to adverse environmental conditions since many of the species occur in semi-arid or cold (Andean páramos) areas. Eleutherodactylus is generally thought to be the stock from which Euparkerella, Noblella, and Sminthillus evolved (Griffiths, 1959) and from which Syrrhophus and Tomodactylus are derived (Firschein, 1954).

The present distribution of Hylactophryne (isolated on the Mexican Plateau) and its digital form (like that of Papuan and many primitive South American leptodactylids) suggest that the genus was isolated in México throughout the Tertiary, whereas the other Central American genera are either post-Pliocene derivatives of Eleutherodactylus or invaders of Central America from South America since the mid-Pliocene land bridge was formed (Lloyd, 1963).

Piatt (1934) presented arguments against assigning Eleutherodactylus latrans to the genus Lithodytes and concluded that it was a "true" Eleutherodactylus. Contrary to his arguments, latrans (= augusti of Zweifel) and E. tarahumarensis Taylor differ from all other Eleutherodactylus (and Syrrhophus and Tomodactylus) in the nature of the tips of the digits (external and skeletal). The digits of Hylactophryne are like those of Eupsophus. My study of nearly all genera of leptodactylids indicates that Noble (1925) was correct in suggesting that Borborocoetes (= Eupsophus) is a close relative of Eleutherodactylus latrans, although Noble's arguments were based in part upon false evidence concerning the breeding habits of E. latrans, then thought to have a free-living tadpole.

Kellogg (1932) and Piatt (1934) argued that the terminal phalanges of E. latrans were typically eleutherodactyline. The variation of this character in Eupsophus (see Fig. 4) ranges from knobbed to bifurcate or Y-shaped (T-shaped in Eleutherodactylus, Syrrhophus and Tomodactylus) and encompasses the nature of the character represented in Hylactophryne. Eupsophus differs from Hylactophryne in possessing a frontoparietal fontanelle, in generally having a maxillary-quadratojugal gap, and in having a free swimming tadpole stage.

KEY TO MEXICAN LEPTODACTYLID GENERA

1. Small (20-40 mm.), pustular, toadlike frogs; maxillary and premaxillary bones not bearing teeth Engystomops

Large (20-110 mm.), smooth skinned and non-toadlike frogs; maxillary and premaxillary bones bearing teeth 2

2. No conspicuous waist (Fig. 5); sternum bearing bony style, Leptodactylus

Constrictions at waist (Fig. 5); sternum cartilaginous, no bony style 3

3. Few (less than six), if any, supernumerary tubercles on plantar surface Eleutherodactylus

Many (more than 8) supernumerary tubercles on plantar surfaces 4