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(Sakai, 1963)

The carapace of this new species is broadly oval in outline, the dorsal surface is rather depressed, thickly covered with obscure tubercles. There are eight protuberances on the dorsal surface, of which two are in the median line and the remainder are disposed symmetrically on either side. Of these symmetrical protuberances, the protogastric ones are the largest and are markedly convex, the two anterior branchial ones are moderately large, while the inner branchial ones are small and only slightly convex. The metagastric area is depressed and low, the cardiac region is also very small and low, while the intestinal region is moderately convex.
The front is obtusely produced beyond the outline of the carapace and its anterior edge is obscurely bilobed. The antero-lateral and postero-lateral borders are continuous, marked with eight low triangular lobes, which are in contact with each other at their bases. The posterior border is a little broader than the front and is obscurely cristate.
The anterior extremity of the buccal frame is, contrary to the usual character of the American species, not at all pointed, the median portion of the anterior edge of the buccal frame is subtruncate or sinuate; on either side of this ridge the efferent branchial orifices open. The external maxilliped has the merus distinctly shorter than the ischium, the exopodite is narrow and its tip not much exceeding the junction between the ischium and merus. The truncate anterior margin of the merus is obscurely divided into two processes, the outer one of which is somewhat dilated and obscurely bifid, fitted to the efferent branchial orifice, while the inner one is short and rather transverse, and its anterior edge is fitted against the median edge of the buccal frame between the two efferent branchial orifices.
The chelipeds are symmetrical, the merus is flattish, almost concealed beneath the expanded antero-lateral borders of the carapace; the carpus is enlarged, its antero-internal edge is produced into a tooth; the propodus is high, its upper inner edge bears two obtuse teeth, while its lower edge is armed with three pointed teeth. On the lower margin of the broad immovable finger there is a proximal expansion bearing three teeth on its free edge; the movable finger is rather slender.
The ambulatory legs are compressed, the merus has two teeth on the posterior edge, the carpus has a prominent tooth on the anterior border; the propodus of the anterior two pairs is armed with three teeth on the anterior border, and two teeth on the posterior border, whereas in the third pair, both borders are armed with two teeth. In the last pair, the teeth on both borders are obscure. All the dactyli are compressed; in each of the anterior three pairs the posterior edge has two distinct teeth, whereas in the last pair these teeth are obsolescent.
The abdomen of the female holotype is rugose, its terminal segment is broadly triangular, the length not exceeding the breadth.
Measurements: Length of carapace 19 mm, width of same 15 mm. (T. Sakai, 1963)

Type locality: Okino-yama, off Misaki, Sagami Bay, Japan, 80 m.
Range: Japan - Okino-yama, off Misaki, Sagami Bay (Sakai, 1963, 1965, 1976); Kumano-nada (Miyake, 1983).

Sakaila imperialis