Cryptocellus sofiae sp. nov. is described based on males and females obtained from the easternmost part of Colombia, in Vichada Department. The new species is placed in the adisi species-group, based on the morphology of the male copulatory apparatus and the presence of polygonal (navicular or calyx-like) setae. With this addition, the group now comprises four species. A key for the identification of the members of this group is provided. Some taxonomic remarks about the adisi group and the genus Cryptocellus Westwood, 1874 are made.