Abstract
Distribution of BL (bluish body-color type) and DA (dark body-color type) populations of the Japanese freshwater crab Geothelphusa dehaani (White) was investigated in the middle reaches of the Tama River, mainly in Hachiohji City in the south-west area of Tokyo. On the right bank of the Tama River, DA populations were found in the upper streams of and on the north of the Asakawa River which is one of the major tributaries of the Tama River. On the other hand, BL populations were distributed on the south of the Asakawa River, including Tama Hills. On the left bank of the Tama River, BL populations were found at Todoroki, Meguro-ku and Ohkura, Setagaya-ku , and a DA population was found at Ohsawa, Mitaka City, Tokyo. A DA population was also found at Miyadera, Iruma City, Saitama Prefecture. One Mixed population was found at Tatemachi, Hachiohji City.
