R. lamasi, ranked as “least concern” (LC) on the Red List, inhabits the eastern versant of the Cordillera Azul in the Departamentos Pasco and Huánaco in the eastern central Peru, at 300-1,700 m above the sea level. It lives in primary lowland and both primary and secondary premontane forest. It has been discovered in the lowlands near Iscozacín at around 350 m a.s.l., with annual amounts of precipitation of 1,000-2,000 mm, where it lives in leaf axils of bromeliads growing in high forest, whereas at 670 m it inhabits bamboo forests. There, the forest in most cases consists of small, thin trees, and relatively common epiphytic plants. The annual amount of precipitation in these areas varies between 6,000 and 7,000 mm. There are also some bamboo thickets at about 1,700 m that appear to be inhabited by this species.
The males usually grow up to 17.7 and the females up to 19.9 mm. Specimens from individual known populations may look very dissimilar.
The individuals from Bosque Castilla near Iscozacín have a black body with a pattern consisting of yellow lines of which one extends across the snout right in front of the eyes. From its center springs a median stripe that continuous further to the cloaca. A supralabial stripe passes below the eye and then extends towards the groin in the shape of a dorsolateral stripe. A thin line across the sacrum links both the median and the dorsolateral stripes. The light yellow or gray ventral side has large, irregular, black spotes that cannot be seen in the anterior part of the throat. A black crossbar to separate the gular from the chest coloration is also not present. Light gray limbs have some irregular black spots.
The frogs from the pass area between Tingo María and Aguaytía are largely yellow above. There is a black spot on the snout that also includes the nostrils. From the eyes to the groin area of the respective side, there extend two wide black dorsolateral stripes that are often in contact in mid-back. The frogs’ black sides contrast with the light blue ground color of the ventral side. On the chest and on the throat, a yellow spot can be seen. There are also some large black spots that may sometimes merge to form an irregularly shaped crossbar in the posterior gular region, while the light blue limbs are marked with large black spots.
The species feeds on small and large fruit flies, aphids, springtails, small crickets, white woodlice, firebrats, flourmoth caterpillars, etc.
For breeding, the terrarium of the Type I is most appropriate with the temperatures around 22˚C during the day and only slightly lower at night. This species also requires a high level of humidity, whereas when using a fogger, the frogs tend to be more active.