The Leyden Museum received some weeks ago from Mr. Kleiweg de Zwaan a lot of Insects collected by him in the island of Nias. In this collection I found a male and a female of an interesting Longicorn, viz. Nothopeus hemipterus Oliv. (also known from Java, Burma and Northern India) captured on Mount Sitoli, together with both sexes of a fossorial Hymenopteron belonging to the family Pompilidae, viz. Macromeris splendida Lep. Pompilus coriarius Taschb.) which wasp perfectly resembles the beetle, both insects being black with a strong metallic blue hue especially on the wings. Undoubtedly this is a not yet recorded case of protective resemblance between Longicorns and Fossorial Hymenoptera. As yet the following eight species are known in the genus Nothopeus and, certainly, they all will have their model.