Holotype.—UMMZ 101121, adult male from a cave near El Pachón, 8 km. N Antiguo Morelos, Tamaulipas, México, 250 m., collected on March 13, 1949, by Paul S. Martin.
Paratopotypes.—(26). UMMZ 101122 (10), 101123 (2), 101126, 126993 (12).
Diagnosis.—Medium-sized frogs, males 22.8-28.4 mm. snout-vent, females 25.9-32.0 mm. snout-vent; vocal slits in males; digital tips greatly expanded, more than twice width of digit; first finger shorter than second; skin of dorsum shagreened to pustular, that of venter weakly to moderately areolate; toes webbed basally; dorsum light brown to tan with brown vermiculations; venter white; diameter of tympanum 53.9 to 64.2 per cent that of eye in males, 50.6 to 58.7 per cent in females.
Description and variation.—([Fig. 12]). Head wider than body; head as wide or wider than long in males, sometimes longer than wide in females; snout acuminate in dorsal view, elongate and rounded in lateral profile; canthus rostralis rounded but distinct; loreal region slightly concave, sloping abruptly to lip; lips not flared; eyelid about two-thirds interorbital distance; length of eye less than distance between eye and nostril; diameter of tympanum 53.9 to 64.2 per cent that of eye in males, 50.6 to 58.7 per cent in females; tympanum round and distinct in both sexes; supratympanic fold moderately distinct; choanae within border of jaws, completely visible from directly below, rounded to slightly oval; dentigerous processes of prevomers and teeth absent; tongue free for posterior one-half, generally oval in outline; vocal slits present in males.
Many scattered pustules on dorsum; flanks areolate; skin of venter areolate or not (variability may be due to differences in preservation); ventral disc distinct on chest and lower abdomen; inguinal gland present or not, when present varying from very large and distinct to poorly defined; axillary gland absent.
First finger shorter than second; all fingers bearing truncate tips with pads, each pad having a terminal groove; fingers fringed; fingers three and four having dilated pads two to three times width of digit; subarticular tubercles large, conical, rounded, simple; supernumerary tubercles numerous on thenar surface, none on digits; three palmar tubercles, outer slightly smaller than largest supernumerary tubercles; row of tubercles on outer edge of forearm variable, weak to very distinct; tips of toes wider than digits, rounded to truncate at tips, each pad having terminal groove; toes having lateral fringes, bases of toes united by web, web not extending to basal subarticular tubercle; subarticular tubercles smaller than those of hand, round, conical, simple; supernumerary tubercles numerous on plantar surfaces, extending between metatarsal tubercles, present on toes between basal two subarticular tubercles in some specimens; outer metatarsal tubercle round, conical, one-half as large as ovoid, non-compressed inner metatarsal tubercle; tarsal tubercles or folds absent.
Ground color pale reddish-brown to tan dorsally, creamy on flanks; dorsal pattern consisting of reddish-brown to brown vermiculations extending onto flanks; distinct interorbital light bar present; loreal region darker than snout, reddish-brown compared to tan or pale reddish-brown; arms colored like dorsum; thighs banded, unicolor brown on posterior surfaces; shanks and tarsi banded; venter white to cream punctated with brown in some specimens.
The variation in proportions is summarized in [Table 5].
Remarks.—Martin (1958) expressed some doubt that this series of 26 specimens was identical with "S. latodactylus." My study indicates that the specimens from El Pachón represent a distinctive but allied species. Males of the two species can be readily separated by the relative sizes of the tympani, presence or absence of vocal slits, and color pattern. Females of the two species can be separated by color pattern. Within the type-series, the pattern varies from weakly to strongly vermiculate but is always recognizable as vermiculate rather than spotted as in S. longipes (= S. latodactylus of Taylor and Martin).