ABSTRACT Megaspiridae include land snails with a tall spire. They occur in Brazil, New Guinea and Australia. Megaspira Lea, 1839 is distributed through the central and southeast regions of Brazil There is controversy regarding the number of species in the genus, and their taxonomic status. The characters used to identify Megaspira include a large cylindrical shell and internal armature in the columella. The goal of the present study is to describe a new species for the genus, based on shell morphology, microsculpture and the inner anatomy. These anatomic characters had not been described before for any of the included species. The material was collected at the Jararaca trail, Ilha Grande (Angra dos Reis, state of Rio de Janeiro). Seven linear measurements were taken from the shells. Megaspira adenticulata sp. nov. differs from the other species of the genus by not having apertural lamella in the shell aperture or in the columella in adult specimens. Also, the shell does not have light brown spots, as observed in other species of Megaspira. The shell has a mean of 16 whorls and height of 27 mm. It is smaller in average size than the shell of other described species. The new species was found under leaf litter, especially near rocks and in shallow soil.