1. Department of Natural History Sciences; Graduate School of Science; Hokkaido University; Sapporo 060-0810 Japan
2. Hiruzen Institute for Geology and Chronology Co., Ltd; 2-5 Nakashima Naka-ku Okayama 703-8252 Japan
3. Research Institute of Natural Sciences; Okayama University of Science; 1-1 Ridai-cho Kita-ku Okayama 700-0005 Japan