The Oosternum convexum species group is defined on the basis of external morphological characters. Three species are recognized within the group, all of them endemic to the Cordillera de Talamanca Mts. in Central America: O. convexum sp. nov. (Panama, Costa Rica), O. intermedium sp. nov. (Costa Rica) and O. simplex sp. nov. (Costa Rica).
A key to species is provided, along with drawings and SEM photographs of diagnostic characters.