The male and female external genital structure of Aenetus virescens (DOUBLEDAY) are described and figured. The musculature of male external genitalia is also analyzed. On the male external genitalia, the following character-states are characteristic; 1) the absence of mesosome, 2) valva with an acutely pointed long process at the middle portion of its ventral margin. On the musculature of male external genitalia, the m.5 (vinculum-valva) is very broad and well developed. Some types of mesosome in the male genital structure of Hepialidae are shortly discussed.