Ortmann, 1892
The carapace subcircular and discoidal, the upper surface being very smooth and depressed. There is almost no indication of regions besides a pair of very indistinct branchio-cardiac grooves. The front is much less produced beyond the eyes and is obscurely bidentate, the postfrontal surface depressed. The hepatic facets are ill-defined, in rear of which the marginal rim of the carapace is finely granulated under the lens. The epistome and the anterior boundaries of the pterygostomial regions are markedly produced and are visible in dorsal view, the latter are shallowly cleft near the outer angle.
The chelipeds in full-grown male are very long and slender, they are much more than 2.5 times the length of carapace. The arm is proximally constricted, where the upper surface is very finely granulated; the palm is flattened and smooth, its inner and outer borders are smooth and not granulated or milled. The fingers are longer than the palm and their cutting edge is finely denticulated in their whole extent. The ambulatory legs are very slender and smooth.
Speaking of the abdomen of male, this species seems to be most primitive of all the Japanese species of this genus; the first and second terga are short but independently movable; the sixth and seventh terga are also freely movable, the former with a tooth near the middle point, which sometimes is rudimentary. Anterior pleopod of male was figured in my previous papers (1934, 1936). Abdomen of female consists of five pieces, the first being completely concealed beneath the posterior border of the carapace and the third to sixth terga are fused together. (Sakai, 1937)
Type locality: Tokyo Bay, Japan.
Range: Japan - Tokyo Bay (Ortmann, 1892), Shimoda (Sakai, 1935), Sagami Bay, Shimoda and Nagasaki (Sakai, 1937a), Amakusa, Sea of Ariake and Niigata (Miyake et al., 1962), Sagami Bay (Sakai, 1965b), Nemuro, Sagami Bay, Manazuru, Mikawa Isshiki, Kii Nagashima, Kii Minabe, and Tosa Bay (Sakai, 1976a), Ogasawara-shoto (Takeda, 1977a), Yamagata Prefecture (Suzuki S., 1979), Shiono-misaki (Takeda, 1979a), Nemuro (Komai et al., 1992); Korea - Pohang and Hae-undae (Kim, 1973).