_Distribution of genus._--Most of lowlands of México and Central America, in some places to elevations of nearly 2000 meters, southward from southern Sonora and Río Grande Embayment of Texas, including such continental islands as Isla Cozumel, México, and Isla Popa and Isla Cebaco, Panamá, to northern South America, where known from Caribbean coastal regions and valleys of Río Cauca and Río Magdalena in Colombia, and Pacific slopes of Colombia and northern Ecuador.
1. Larger frogs ([M] to 76 mm., [F] to 90 mm.) having broad flat heads and a dark brown or black postorbital mark encompassing tympanum 2
Smaller frogs ([M] to 45 mm., [F] to 64 mm.) having narrower heads and lacking a dark brown or black postorbital mark encompassing tympanum 4
2. Lips barred; flanks cream-colored with bold brown or black mottling in groin; posterior surfaces of thighs brown with cream-colored flecks _S. baudini_, p. 289
Lips not barred; narrow white labial stripe present; flanks not cream-colored with bold brown or black mottling in groin; posterior surfaces of thighs variable 3
3. Flanks and anterior and posterior surfaces of thighs dark brown with large pale blue spots on flanks and small blue spots on thighs _S. cyanosticta_, p. 303
Flanks cream-colored with fine black venation; posterior surfaces of thighs pale brown with or without darker flecks or small cream-colored spots _S. phaeota_, p. 308
4. Fingers having only vestige of web; diameter of tympanum two-thirds that of eye; dorsum pale yellowish tan with pair of broad dark brown stripes _S. puma_, p. 314
Fingers about one-half webbed; diameter of tympanum about one-half that of eye; dorsum variously marked with spots or blotches 5
5. Snout short, truncate; vocal sacs in breeding males dark gray or brown; blue spots on flanks and posterior surfaces of thighs _S. sila_, p. 318
Snout long, sloping, rounded; vocal sacs in breeding males white; cream-colored or pale blue flecks on flanks and posterior surfaces of thighs _S. sordida_, p. 323
1. Pond tadpoles; tail about half again as long as body; mouth anteroventral 2
Stream tadpoles; tail about twice as long as body; mouth ventral 5
3. First upper tooth row strongly arched medially; third lower tooth row much shorter than other rows; dorsal fin deepest at about two-thirds length of tail; tail cream-colored with dense gray reticulations _S. puma_, p. 314