A. grinbergsi sp. n, (d holotype, 9 allotype: Los Ulmos, Valdivia, Chile) is described and figured, and a comparison is made of the new sp. and the closely related A. gayi. The main characteristics of the new sp. are: Light spots between ocelli and antennal bases united; a narrow line running backwards to the light margin. In the d the dorsal black does not reach the rear margin of abd. segm. 7. Outer side of femora is nearly completely black. The new sp. seems to oviposit exclusively on the fern, Blechnum chilense. The type material is in the ’’Landessammlungen fur Naturkunde”, Karlsruhe, GFR.