This genus was erected by Mac Lachlan [Journ. Linn. Soc. XI, p. 261 (1871)] for a group of Indian species described by Walker [Cat. Brit. Mus. Neur. (1853)]. Mac Lachlan gives but a preliminary review of the synonymy of the species which were all described by Walker in such an unintelligible manner, that it is impossible to judge after his descriptions about their synonymy. Some weeks ago Mr. W. F. Kirby communicated me the Ascalaphidae of the British Museum and among them were three cotypes of Walker, which he kindly had compared. They agree very well with Walker’s descriptions and belong to the species insimulans, immotus and dicax. As the individuals vary very much in colour after the degree of maturity and as the species have a very large geographical distribution, it is clear why Walker has described under so many names so few species. I refer to them after Mac Lachlan’s synonymy: so is insimulans the male of name has the priority. dicax, which latter Immotus is a distinct species which is synonymical with Ascalaphus cervinus Hagen, from Ceylon. The latter name has, after a cotype of Brauer’s collection in the Vienna Museum, the priority. The same species is figured by Westwood (Trans. Ent. Soc. Lond. 1888). It has a large distribution being found in the Malay Peninsula, Sumatra, Java, Celebes etc. I saw in the Vienna Museum a very large specimen from Manilla, which I think to belong to the same species. Gerstaecker (Mitth. Vorpomm. und Rügen, XXV) described females from Java and Sumatra under the name Suphalasca placida. I cannot give any information about H. verbosus and profanus Walker, quoted by Mac Lachlan as distinct species, but after the descriptions I presume that they are large specimens of cervinus Hagen; I have, however, no original specimens for comparison. H. ctenocerus Gerst. is Acheron trux Walk., as I could state after comparing the types. H. philippinensis v. d. Weele is an aberrant species spread over the Indian Archipelago; it is known from Java, Celebes and Luzon. Leyden, November 1905.