(Sakai, 1965)
Compared with Medaeus serratus, the carapace of this species is narrower and the dorsal surface clearly areolated and granulated. The protogastric areolae are divided into two lobules in the anterior half, the hepatic and branchial areolae are well delimited but never subdivided; the granules found on the anterior portion of such areolae are somewhat large and thick.
The front is unusually prominent and is divided by a deep median V-shaped sinus into two obliquely truncated lobes. The inner anterior angle of each lobe is rounded, the posterior triangular one is separated by a deep sinus from the preorbital tooth. There are two fissures in the upper orbital margin and the external orbital tooth is prominent and acuminate. The two inferior orbital teeth are rather large and are visible in dorsal aspect beyond the eye.
Of the teeth on the antero-lateral borders, the posterior three are large and triangular, located on the level of the branchial surface, while the anterior two are small and subhepatic, situated on the ridge leading to the antero-external angle of the buccal frame. The postero-lateral borders are rather concave; the inner surface of these borders is covered with raised granules interspersed with plumed hairs.
The chelipeds are massive and long; the merus is rather thin, the carpus is massive and marked with small shallow facets enclosed by series of tiny granules and its inner angle bears a rather prominent tooth, followed by a few small accessory ones; the propodus is also massive and granulated, dorsally sulcate and its thin inner edge is armed with about four teeth; the dactylus is dorsally keeled, its prehensile edge is armed with about four teeth; the tips of the fingers are sharply pointed, not hollowed.
The ambulatory legs are very thin and compressed, and the anterior border of the merus, carpus and propodus is carinate; the carina of the merus is very indistinctly dentate with a deep subterminal sinus; that of the carpus has two broad lobes, while that of the propodus has a large proximal lobe. The posterior edge of these segments is finely granulated and plumose. The dactyli are very slender and as long as the propodus, and their tips are acuminate and curved.
The anterior and posterior pleopods of the male are figured in fig. 3c, d, the oblique apex of pleopod 1 bears several longish feathered setae. (Sakai, 1965)
Type locality: south Amadaiba, off Hayama, Sagami Bay, Japan, 85 m.
Range: Cocos-Keeling Islands (Serène & Umali, 1972); Japan - Sagami Bay (Sakai, 1965a), Sagami Bay and Tosa Bay (Sakai, 1965b), Sagami Bay, Kii Minabe and Tosa Bay (Sakai, 1976a), Shiono-misaki (Takeda, 1979a), Kushimoto (Miyake, 1983); Banda Sea (Guinot, 1967c); Australia - off Cape Moreton (Griffin, 1972); 65-85 m.