Circulium rotundatum (Hess, 1865), comb. nov. (Figures 5, 6) Sesarma rotundata Hess, 1865, p. 149, pl. 6, fig. 9 [type locality: ostensibly Sydney]; Miers 1877, p. 136 (part); Haswell 1882, p. 108; De Man 1896, p. 110, pl. 3, fig. 6, 6a. Sesarma dentifrons A. Milne-Edwards 1869, p. 31 [type locality: Samoa]; De Man 1896, p. 110, pl. 3, fig. 7, 7a, b. Sesarma oceanica De Man, 1889, p. 429, pl. 10, fig. 9 [type locality: Ponape Island]. Sesarma gardineri Borradaile, 1900, p. 593, pl. 42, fig. 8 [type locality: Funafuti and Rotuma islands]. Sarmatium faxoni Rathbun, 1906, p. 841, pl. 7, fig. 1 [type locality: O’ahu, Hawaiian Islands, and Marshall Islands]. Sesarma (Sesarma) rotundatum: Rathbun 1907, p. 33. Labuanium rotundatum: Serène and Soh 1970, p. 401; Davie 2002, p. 221; Ng and Liu 2003, p. 614 (part), fig. 8E–I; Ng et al. 2008a, p. 221 (list); Ng and Davie 2011, p. 43 (part); Ng 2012, p. 266, figs 1–7 [neotype designated; type locality: Niuafou Island]. Material examined Neotype. USNM 1150304, male, 36.3 × 36.3 mm, Niuafou Island, Tonga, coll. H.C. Kellerr, Naval Eclipse Expedtion, 29 September 1930. Others. ZRC 2002.0453, 1 male, 24.4 × 23.7 mm, Swain’s Island, coll. Itasca Expedition, March 1936; ZRC2012.0398, 5males,19.7× 20.1–28.8× 30.9 mm, 3females,23.8 ×24.7–30.0 × 31.6 mm, on trees, Renipiua Island,small island on the southern end of Pohnpei atoll,ca. 6.7449°N, 157.953° E, coll. T. Herman via B. Lynch, caught at night using headlamps, 2 July 2011. Diagnosis Two pairs of postfrontal lobes present, lateral lobes exceeding mesial lobes anteriorly, anterior edge of lobes close to but never reaching frontal margin in dorsal view. Epistome posterior margin with 3 low lobes, lateral lobes terminally directed anteroventrally, median lobe terminally directed anteriorly. Chela outer surface sparsely covered with large granules; upper surface with 1 complete longitudinally traversing row of small granules. G1 relatively more slender, relatively long, straight proximally, distally bent about 60–80° against main axis; distal beak-like and corneous process relatively long, narrow. Sternal vulval cover covering almost entire vulva, produced anteroventrally as trigonal pyramid projection. Colouration In life, carapace and pereopods uniformly yellow to orange; eyes white; chelae orange to yellow, with white fingers (Ng 2012, fig. 1). Distribution South Pacific: Cook Islands (Ng 2012); American Samoa (Ng 2012); Samoa (Milne-Edwards 1869); Tonga (Ng 2012) [type locality: Niuafou Island]; Funafuti and Rotuma Islands (Borradaile 1900). Micronesia: Marshall Islands (Rathbun 1906, 1907); Pohnpei (De Man 1889). Ostensibly Sydney, Australia (see McCulloch 1913, p. 323; Davie 2002, p. 221; Ng 2012, p. 268). The record from O’ahu, Hawaiian Islands (Rathbun 1906, as Sarmatium faxoni) has been questioned (see Ng 2012). Ecological note The species has nocturnal habits and has been found on large trees, including coconut trees, living in the foliage (Brian Lynch, personal communication).

Published as part of Naruse, Tohru & Ng, Peter K. L., 2020, Revision of the sesarmid crab genera Labuanium Serène and Soh, 1970, Scandarma Schubart, Liu and Cuesta, 2003 and Namlacium Serène and Soh, 1970 (Crustacea: Decapoda: Brachyura: Sesarmidae), with descriptions of four new genera and two new species, pp. 445-532 in Journal of Natural History (J. Nat. Hist.) (J. Nat. Hist.) 54 (7 - 8) on pages 458-460, DOI: 10.1080/00222933.2020.1763491, http://zenodo.org/record/4609148