258 
THE VOYAGE OF H.M.S. CHALLENGED. 
margins. The dorsal surface plicated only on the lateral margins. Front very broad, 
deflexed, with the anterior margin straight or slightly sinuated. Orbits small, with the 
interior subocular lobe usually very broad, reaching the front, and completely excluding 
the antennae from the orbit. Epistoma very short, almost linear-transverse. Endostome 
with the longitudinal ridges usually (but not invariably) distinctly developed. Post- 
abdomen (in the male) distinctly seven-jointed, and covering the whole width of the 
sternum at the base. Eye-peduncles short, robust. Antennules transversely plicated in 
short, wide fossettes. Antennae with the basal joint very short, completely excluded 
from the orbit, and more or less produced at its antero-external angle ; flagellum short. 
Exterior maxillipedes with a rhomboidal gape; the merus-joints short, and broader than 
in Grapsus, distally truncated, and bearing the next joint at their summits, near the 
antero-external angle. Chelipedes subequal, and moderately developed, with the merus- 
joints trigonous and their anterior margins distally dentated; palms somewhat turgid, 
rounded above and below; fingers excavated at the distal extremity. Ambulatory legs 
of moderate length, with the merus-joints dilated and compressed, their anterior margins 
with a subterminal spine, and their posterior margins with several spines at the distal 
extremity; the dactyli rather short and spinuliferous. 
This genus is distinguished from P achy grapsus, its nearest ally, by the less convex 
carapace, which is usually less distinctly plicated on the dorsal surface, and by the great 
development of the interior subocular lobe of the orbit. The species, which with their 
synonyms have been enumerated by Mr. Kingsley, are apparently confined to the Indo- 
Pacific region. 
Metopograpsus messor (Forskal). 
Cancer messor, Forskal, Descript, animalium quae in itinere orientali observavit, P. Forsk&l, 
p. 88, 1775. 
Grapsus gaimardii, Audouin, Explic. des plancbes in Savigny, Descr. de l’Egypte, Crust. Atlas, 
pi. ii. fig. 3. 
,, messor, Milne Edwards, Hist. Nat. Crust., vol. ii. p. 88, 1837. 
Metopograpsus messor, Milne Edwards, Ann. d. Sci. Nat., tom. cit., p. 165, 1853. 
„ ,, Kingsley, tom. cit., p. 190, 1880, and references to synonyma. 
Grapsus (Pachy grapsus) adluopicus, Hilgendorf, Crust, in Yan der Decken, Reise in OstAfrika, 
vol. iii. p. 88, pi. iv. fig. 2, 1869; teste, Hilgendorf, Monatsber. d. k. preuss. 
Akad. d. Wiss. Berlin, p. 808, 1878. 
Metopograpsus messor, var. frontalis, Miers. 
Metopograpsus messor, var. frontalis, Miers, Ann. and Mag. Nat. Hist., ser. 5, vol. v. p. 311, 1880. 
Kanclavu, Fiji (a small male) ; Tahiti, near the reefs (two males and two females) ; 
Papiete, Tahiti, in brackish water at the mouth of a stream (several specimens, mostly 
females) ; Sandwich Islands, Hilo, on the beach (several males and females). 
