Stimpson, 1858
The carapace is pentagonal in outline, much broader than long, the proportion between length and width being as 1: 1.33. The upper surface is perfectly smooth and polished, the margins of the carapace, excepting the fronto-orbital margins, are developed into lamelliform expansions of which those on the hepatic margins are narrow and horizontal, while those on the postero-lateral borders are very broad and bent upward, so that the upper surface of the carapace appears very low.
The front is obtusely triangular, bending upward, with a median ridge on the upper surface, running from the tip to the middle of the gastric region.
The infraorbital tooth is indistinct, and is fused with the anterior boundary of the pterygostomial region. The anterior extremity of the buccal cavern projects beyond the level of the anterior boundaries of the pterygostomial regions. The merus of the external maxillipeds is shorter than the ischium and is pointed at the tip; the exopodite is broad and foliaceous as in the genus Philyra.
The chelipeds are symmetrical, each segment is flattened and has lamelliform expansions on both borders as on the margins of the carapace, the fingers are very short and stout. The ambulatory legs are concealed beneath the lamelliform expansions of the carapace when retracted; merus, carpus, and propodus are respectively crested with laminae, while dactylus alone is slender and acuminate.
The abdomen of male is narrow triangular, consisting of four pieces, its formula being as 1 + 2 + R + T. (Sakai, 1937)
Type locality: Kagoshima Bay, Japan.
Range: Japan - Kagoshima Bay (Stimpson, 1907), Nagasaki (Sakai, 1937a), Amakusa and Sea of Ariake (Miyake et al., 1962), Kagoshima Bay, coast of Amakusa, Nagasaki, and Goto-retto (Sakai, 1976a), Oshima Passage, Amami-Oshima (Takeda, 1989).