Revisionary studies on the enigmatic neotropical ant genus Stegomyrmex Emery, 1912 (Hymenoptera: Formicidae: Myrmicinae), (with the description of two new species - Feitosa, Rodrigo dos Santos Machado; Brandão, Carlos Roberto Ferreira; Diniz, Jorge Luis Machado (Journal of Hymenoptera Research, 2008)