Takeda & Tachikawa, 1995
Description of holotype: Carapace narrowly ovate; its dorsal surface strongly vaulted in both directions as a whole, especially so for its posterior half and lateral parts, engraved into regions by a series of broad deep, circumferential and interregional grooves. Regions thickly paved with smooth, truncated or weakly convex granules of polygonal shape and various sizes, their margins partly overhanging interregional grooves as thin roofs; bottom of grooves frosty, with small obtuse granules mixed with raised mushroom-like granules of good size. Frontal region rather quadrate, divided into two by a median, longitudinal shallow furrow, covered with smaller granules; its posterior median part connected with anterior prolongation of mesogastric region by a narrow bridge. Supraorbital region forms a rounded lobe separated from outer prolongation of frontal lobe and also from inner prolongation of first lateral tooth of carapace each by a deep notch and a vestigial suture. Anterior prolongation of mesogastric region slowly widening posteriorly toward lateral angles, with weakly concave lateral margins, and then narrowing toward constriction between meso- and metagastric regions. Metagastric region completely confluent with mesogastric region, without trace of dorsal groove or even depression, its lateral margins being inclined inward, nearly parallel to lateral margins of mesogastric region. Protogastric region more or less longitudinally ovate, concave at its antero-lateral part faced to first lateral tooth, bordered on anterior prolongation of mesogastric region for its inner median third; its outer margin zigzag in accordance with pavement, distinctly isolated from branchial region by a deep, wide oblique groove. Cardiac region rather quadrate, only slightly wider than meso- and metagastric regions, weakly convex dorsally as a whole, with zigzag lateral margins, being separated from posterior margin of metagastric region by a transverse, narrow but deep groove. Intestinal region transverse, perpendicularly directed downward so as to give a false impression of posterior margin of carapace in dorsal view. Branchial region much more strongly raised than other regions, oblique and very weakly concave along anterior inner margin faced to protogastric region, nearly longitudinal along inner margin faced to meso- and metagastric regions, deeply concave along outer margin faced to third lateral tooth of carapace.
Lateral margin of carapace divided into four teeth which are directed obliquely downward and clearly cut off from protogastric, branchial and cardiac regions by a circumferential, deep submarginal groove being in connection with other interregional grooves. First tooth regularly convex in dorsal view, but its true margin more strongly directed downward, subtruncated, with weakly angulated posterior end; outer margin of circumferential groove deeply excavated outward so as to form an ovate concavity at anterior dorsal part of first tooth. Second tooth separated from the first by a deep U-shaped depression in dorsal view; in lateral view this depression longitudinal, forming a deep groove extending just to posterior corner of buccal frame. Subhepatic groove rather narrow, but deep, originating from longitudinal groove between first and second teeth and extending anteriorly just to level of anterior part of buccal frame. Pterygostomial region thus formed narrowing distally, covered thickly with conical granules of various sizes. Second tooth nearly conical in dorsal view, with angulated tip, but its anterior margin weakly concave near anterior end, making a bilobate appearance as a whole. Third tooth subequal to the second, with regularly convex tip, divided from it by a wide notch; its posterior margin very shallowly concave near posterior end. Fourth tooth oblique in front of lateral end of intestinal region, nearly conical and more or less angulated at median part in dorsal view; its posterior martin almost transverse or directed rather anteriorly, tip of fourth tooth failing to reach to level of intestinal margin in dorsal view. Lower surfaces of second to fourth teeth deeply excavated so as to be wing-like as a whole, covered with mushroom-like granules of various sizes as well as pleural surface; lower surfaces of second and third teeth and pleural surface with three rows of several granules of good size directing toward base of ambulatory legs from margins of teeth, viz., one from tip of second tooth and two originated from tip of third tooth; boundary of second and third teeth and also that of third and fourth teeth indicated by a small ovate hole opened to dorsal submarginal groove.
All appendages missing. (Takeda & Tachikawa, 1995)
Type locality: Kominato, Chichi-jima, Ogasawara-shoto, 7-8 m.
Range: Japan - Ogasawara-shoto (Takeda & Tachikawa, 1995).