Binomial Name: Beddomea albizonata/Beddomea albizonatus
Beddomea albizonata is an endemic species of land snails found in lowland wet zone forests of Sri Lanka. Green colored shell is an adaptation for the arboreal life. This snail can be mostly found on wet surfaces of rocks and leaves where the humidity level is high. Above photographs were taken at Kalugala and Makandawa rain forests. I observed that they are active when the environment is wet and if the habitat is getting drier they moved into the shell and hibernated like in the last picture.
Reference: http://www.nhm.ac.uk/research-curation/research/projects/tropical-land-snails/publications.dsml