I have studied on species of Trombicula developing at contaminated area by Rickettsia orientalis since 1953. So called "Umayado Disease" which proved severe signs usually has happened every year at summer especially at the east area of Kagawa-ken, and this disease was analysed by Dr. NOKIHARA by its serological intemes performed eagerly to prove the original nature of the disease, and has proved that so called "Umayado Disease" was nothing but "Tsutsugamushi Disease". This time, I have investigated the agencies comtaminating and spreading the Rickettsial agent, and have developed Trombicula which analysed 3 Genus and 10 species as follows, 1) Trombicula (Leptotrombidium) Kitasatoi FUKUZUMI et OBATA, 1950 2) Trombicula (Leptotrombidium) tosa SASA et KAWASHIMA, 1951 3) Trombicula (Leptotrombidium) pallida NAGAYO, MITAMURA et TAMIYA, 1919 4) Trombicula (Leptotrombidium) murotoensis SASA et KAWASHIMA, 1951 5) Trombicula (Leptotrombidium) kuroshio SASA et KAWASHIMA, 1951 6) Trombicula (Leptotrombidium) fuji KUWATA, BERGE et PHILIP, 1950 7) Trombicula (Leptotrombidium) miyajimai FUKUZUMI et OBATA, 1950 8) Trombicula (Miyatrombicula) kochiensis SASA, KAWASHIMA et EGASHIRA, 1952 9) Euschongastia alpina SASA et JAMESON, 1953 10) Gahrliepia saduski WAMERSLEY, 1952