(Figs. 43–45)

Material examined. Holotype: male (10.3 × 6.5 mm) (IOCAS), station 6197, 21°00'N 109°00'E, Tonkin Gulf, China. Paratype: China: 1 male (9.0 × 5.6 mm) (ZRC 2012.1033), station 6214, 20°45'N 108°30'E, coll. cruise boat 228, 15 February 1960.

Diagnosis. Carapace subquadrate, about 1.5 times as broad as long, dorsal surface granulated; regions indistinct, with shallow median H-shaped depression (Fig. 43A). Anterolateral margin arcuate; posterolateral margin with angled prominence over base of posterior pereopods (Figs. 43A, 45A). Front deflexed, divided into 2 lobes, not projecting beyond edge of orbits (Fig. 43B). Eye slightly movable, small, cornea pigmented, wider than peduncle. Pterygostomial region with row of oblique striae (Figs. 43B, C, 45B). Third maxillipeds broad (Figs. 43C, 44A, 45E), completely covering buccal cavity; ischium slightly longer than merus, combined length of dactylus, propodus and carpus slightly shorter than that of merus and ischium; exopod narrow, 0.3 width of ischium, slightly granular, flagellum well developed. Chelipeds asymmetrical (Fig. 44B, C). Fingers gaping when closed, palm of both chela finely tuberculate (Figs. 44B, C, 45G, H). P2–P4 tomentose, surfaces granulated (Fig. 43A); merus of P4 3.5 times as long as broad, shallow longitudinal groove on outer surface medially; dactylus of P4 gently upcurved. Male thoracic sternum relatively broad (Figs. 44A, 45C, D), surface finely granular; sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternite 3 separated from sternite 4 by distinct ridge; transverse sternal groove extends obliquely from edge of sternoabdominal cavity, almost reaching base of chelipeds (Figs. 44A, 45C, D); sternite 8 exposed, triangular, slightly shorter than abdominal somite 1; sternoabdominal cavity reaching middle to thoracic sternite 4 (Figs. 44A, 45C). Male abdomen relatively narrow (Figs. 44A, 45F), surface granular, somites 1 and 2 free; somites 3–5 fused, lateral margin slightly arched; somite 6 as long as wide, lateral margin expanded into blunt triangular projection subproximally; telson subpentagonal, distal margin rounded, sparsely setose. G1 (Fig. 45I, J) S-shaped, distal part tapered, sparse short setae present medially; row of 3 large teeth on lateral margin medially; distal part exposed on thoracic sternal groove, not concealed under abdomen. Female unknown.

Colour. Not known.

Etymology. From the Latin propinqua for close; alluding to the similarity of the new species with M. anfracta.

Remarks. This species closely resembles M. anfracta in the shape of G1 and the tuberculation of carapace, chelipeds and P2 to P4. However, the G1 of M. propinqua, new species, is relatively more slender with a row of three strong teeth on the lateral margin medially (Fig. 45I, J) (G1 is relatively stouter, without the presence of teeth in M. anfracta (Fig. 23F, G). In addition, the carapace and anterior thoracic sternum are also relatively wider in M. propinqua (Figs. 43A, 44A versus Figs. 22A, 23B, C). The telson of M. anfracta is subtriangular while in M. propinqua is subpentagonal, furthermore P2–P4 are shorter in M. anfracta, the merus of P4 is 2.5 as long as wide (Figs. 22A, C) versus 3.5 as long as wide in M. propinqua (Fig. 43A).

Type locality. Tonkin Gulf, Vietnam.

Distribution. Tonkin Gulf, Vietnam. Subtidal.