Sakai, 1934
Carapace nearly or less than twice as broad as long, the surface remarkably uneven, the lateral epibranchial and hepatic regions being convex, but the middle region between cardiac and gastric regions is laterally depressed. Cardiac region transversely convex but the usual ridge, present in the allied species, is almost rudimentary.
Front slightly produced beyond the eyes in normal position and is bilobed. Orbit inclined outward and downward. Antero-lateral borders are finely granulated along the borders and are densely tomentous.
Chelipeds stout, merus granulated along the inner and upper ridges and are pubescent. Immovable finger very short and triangular, a strong tooth is near the base on the prehensile ridge; movable finger very strongly curved down, edge without a tooth and an extensive hiatus is left when the fingers are closed, the hiatus being covered by hairs at the base of the fingers.
Ambulatory legs all slender, especially in the first pair, which is a little longer than the fourth pair. Second pair exceeds the first, third pair strongest but is not so remarkable as in Pinnixia occidentalis Rathbun. Penultimate segment of male abdomen very narrow. (Sakai, 1934b)
Type locality: Mutsu Bay, Japan.
Range: Japan - Mutsu Bay (Yokoya, 1928), Kinkazan, Sioya-zaki, and Owase (Yokoya, 1933), Mutsu Bay, Kinkazan, Siwoya-zaki, Manazuru, Shimoda, Ise By, and Owase (Sakai, 1934b), Mutsu Bay, Sagami Bay and Ise Bay (Sakai, 1939), Tokyo Bay (Sakai, 1955a), Rokkaku River, Saga Prefecture, Nishinotsu, Okinohata, Yanagawa City (Miyake, 1961), Sagami Bay (Sakai, 1965b), Mutsu Bay, off Inubo-zaki, Sagami Bay, Ise Bay, Osaka Bay and coast of Kagawa Prefecture (Sakai, 1976a), Amakusa (Yamaguchi et al., 1976), Sakata, Yamagata Prefecture (Suzuki S., 1979), Otsuchi Bay, Iwate Prefecture (Takeda & Konishi, 1991), Ishikari Bay, Funka Bay, Akkeshi, Kuninui, and off Ohmu, Hokkaido (Komai et al., 1992), Suruga Bay (Takeda, 1997), Matsuyama, Seto Inland Sea (Takeda et al., 2000); Yellow Sea (Takeda & Miyake, 1968c).