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Shen, 1932

Diagnosis: Carapace with its breadth more than one and half times its length. Dactylus of third maxilliped extended little beyond the suture between merus and ischium. Ischium broadened basally. Movable finger of male bearing a large tooth at its middle region, of female bearing two such teeth. Second ambulatory leg largest, its merus bearing coarse and irregular granules on its posterior margin. Sixth male abdominal segment with its basal breadth more than twice its length.

Description: Carapace transversely ovoid. Surface coarsely punctate. Regions ill-defined. A transverse groove situated at its middle region. Many fine oblique wrinkles on its lateral regions.
Front with its anterior margin less than one-fifth the breadth of carapace, slightly convex and smoothly ridged. Surface with a faint longitudinal groove. Postfrontal crests slightly indicated.
Antero-lateral margin of carapace granularly ridged. Behind its middle region, a branch of granulated ridge curved medially and posteriorly to a point above the base of fourth leg not meeting the lateral end of posterior margin. Posterior margin of carapace smoothly ridged but gradually becoming granular when its extends forward to meet the lateral margin.
Orbit with its dorsal margin smoothly ridged, interrupted with frontal margin by an oblique groove. Its ventral margin not well marked, its inner orbital tooth small. Suborbital crest finely granulated, extending laterally to a point just below the outer orbital angle.
Antennula obliquely placed under the front. Antenna situated between the basal segment of antennula and the ventral inner orbital tooth, its basal segment movable, second broader than long, third longer than broad, reaching antero-lateral angle of front, its flagellum twelve segmented, reaching beyond the outer orbital angle.
Epistome very short. Anterior margin of buccal cavity broadly concave on both sides, nearly in line with suborbital crest.
Pterygostomial region smooth, convex, with a median oblique ridge. Its lateral and basal borders each with a granulated ridge extending postero-laterally and meeting together below the lateral end of suborbital crest and again extending horizontally on the lateral surface ofd carapace to the base of third leg.
Third maxillipeds broadly gaping. Ischium broadened basally and slightly longer than broad, its inner margin strongly ridged, distal truncate. Merus longer than broad, its anterior portion broader than posterior, outer margin slightly convex, inner margin strongly and obliquely ridged. Palpus large, reaching distal third of ischium when retracted. Carpus transverse. Propodus triangular in shape. Dactylus articulate on inner base of propodus. Dactylus longer than merus, elongate oval. Propodus and dactylus all bearing very long bristles.
Cheliped symmetrical, of male larger than female. Coxa short. Basi-ischium with distal portion of its anterior margin finely granulated. Merus broadened distally, dorsal margin with a tuft of stiff hairs on its distal portion, inner ventral margin with a larger tuft of similar hairs, outer ventral margin finely granulated. Carpus convex, its inner margin finely granulated and hairy. Palm longer than fingers, its dorsal margin with a fine ridge which is more prominent and finely granulated in female, its ventral margin granularly ridged, its outer surface smooth, with a longitudinal groove near its dorsal margin, a finely granulated ridge on its ventral half, extending from its base to tip of immovable finger where the ridge becomes smooth, its inner surface pubescent, with a scarcely granulated line near its dorsal margin, a hairy ridge at its middle and two depressions on its ventral half.
Fingers of male cheliped broadly gaping, of female very narrowly. Movable finger smoothly ridged on its dorsal surface. Its inner margin hairy, bearing a large tooth at its middle region, granulose on its distal region. Immovable finger granulose on its inner margin. Fingers of female cheliped narrowly gaping. Movable finger with two larger teeth on basal portion of its inner margin, seven small teeth on its distal portion. Immovable finger bluntly toothed.
Of ambulatory legs, second pair longest, third longer than first, fourth smallest. Merus of first leg slender, its dorsal margin concave, finely granulated and scarcely hairy, its posterior margin convex, its dorsal posterior margin finely serrated, ventral posterior finely granulated. Carpus with its anterior margin ridged. Propodus grooved on its dorsal and ventral surfaces. Dactylus sulcated. Merus of second leg very broad, its anterior margin finely granulated and hairy, dorsal posterior coarsely granulated and hairy, ventral posterior granulated. Carpus with its anterior margin ridged, dorsal surface with two granulated ridges. Propodus elongate, its dorsal and ventral surfaces grooved, the former with scattered granules, its anterior margin ridged, posterior prominently granulated. Dactylus sulcated and hairy, its anterior margins finely granulated, posterior margins finely serrated. Merus of third leg with its anterior and posterior margins granulated, the former bearing longer hairs, its posterior surface thickly hairy, terminal segments all bearing longer hairs on their anterior and posterior margins. Merus of fourth leg broadened basally, scarcely hairy on its margins, its terminal three segments also bearing longer hairs on their anterior and posterior margins.
Abdomen of male with its first segment ridged, broadest. Second very short, narrower than first. Third broader than second but narrower than first, its lateral margins convex. Fourth and fifth similar in shape. Sixth with its basal margin concave, slightly convex at middle, distal concave, lateral convex at its basal half. Seventh small, semicircular in shape. Abdomen of female broadly oval, nearly covering whole surface of sternum, anterior margin of sternum in both sexes all granulated. (Shen, 1932: 118)

Type locality: Yantai, Shandong Peninsula, China.
Range: S.E. Siberia - Possjet Bay and Peter the Great Bay (Kobjakova, 1967); Japan - Ise Bay and Onomichi (Sakai, 1939), Tara, Saga Prefecture and Furbe, Shimabara Peninsula (Miyake, 1961), Sagami Bay (Sakai, 1965b), Sagami Bay, Yokosuka, Mikawa Bay, Ise Bay and Onomichi (Sakai, 1976a), Amakusa (Yamaguchi et al., 1976); Korea - Inch'on and Kunsan (Sakai, 1939), Jinhae, Inch'on and Jeungsan (Kamita, 1941), Gunsan, Yuldo Island, Palmi Island, and Gomso (Kim, 1973), Yellow Sea side (Sakai, 1976a); China - Liaodong Peninsula and Shandong Peninsula (Shen, 1932, 1937), Yantai (Shen, 1935), Shandong Peninsula and Liaodong Peninsula (Dai & Yang, 1991); muddy flats.

Tritodynamia rathbuni