A very beautiful and by no means common species of Saturnidae of the tropical region is Actias maenas. In the year 1847 Doubleday has bestowed this name upon a female and a year later a male has been named Actias leto by the same author (Annals of Nat. Hist. vol. 19, pag. 95; Transactions Entom. Soc. London, vol. 5, pag. 1i). Doubleday’s female type originates from Silhet, the male from India Orientalis (very undefinite!). It was unknown to Doubleday and also to Walker, that maenas and leto belong to the same species, the latter giving in the List of spec. of the British Mus. (pag. 1263) a diagnosis of a male Tropaea maenas. After Rothschild’s publication it is unquestionable that the species ought to be named „maenas” and that „leto” is a mere synonym. In the East-Indies the females, which differ very much from the males, seem to be decidedly more numerous than the males. This we understand from the rearing experiments by the late Dr. H. W. van der Weele and from those in the Zoological Gardens at Amsterdam. The Leyden Museum possesses also twice more females than males. The same may be the case in British-India. On the other hand on Celebes the males of a variety seem to be more numerous than the females (Deutsche Entomologische Zeitschrift „Iris”, Jahrg. 1909, pag. 24).