Diagnosis: Small uniformly green frog that can be distinguished by a free prepollex at the base of the thumb with an exposed spine in adult males, a round to truncate snout in profile, dark green bones, and only the parietal peritoneal sheath and heart white (Savage 2002).
Description: This rarely seen small frog has a snout vent length ranging from 17.8 mm to 20 mm in adult males and 20 mm to 23 mm in adult females. The head is as wide as long and appears truncated in profile and semicircular in outline. The eyes are large and protuberant, and the interorbital space between is larger than the diameter of the eyes. The snout has a subovoid outline and appears truncated. The tympanum is indistinct and is directed obliquely upward. Vomerine teeth are present in two small patches that are widely separated and immediately medial to the choanae. The body shape is small and slender. The dorsal skin is granular in texture. Finger and toe discs are truncated. Fingers have small subarticular tubercles but no supernumerary tubercles. Accessory palmar and plantar tubercles are present. Finger I is longer than Finger II; vestigial webbing is present between these two fingers. More substantial webbing exists between the outer fingers in the pattern II 2-3 III 2 - 1 3/4 IV. Toes are moderately webbed, described as I 1-2 II 1-2 III 1-2 IV 2-1 V. An elongated inner metatarsal tubercle is present, but the outer metatarsal tubercle is lacking. No inner tarsal fold. Males possess a white nuptial pad on the lateral margin and dorsal of the thumb base. Frogs of this species possess a free prepollex. In larger males the prepollical spine projects externally (Savage 2002).
The coloration is uniformly green on the dorsum, with white pigmentation on the undersides of limbs. The iris is gray-ivory with a black reticulum. This species has dark green bones and a white heart (Savage 2002).
This species was first described by Taylor (1949).
A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio).